Mega Low Earth Orbit(LEO)satellite constellations can provide pervasive intelligent services in the forthcoming Six-Generation(6G)network via the Free-Space Optical(FSO)InterSatellite Link(ISL).However,the challenges ...Mega Low Earth Orbit(LEO)satellite constellations can provide pervasive intelligent services in the forthcoming Six-Generation(6G)network via the Free-Space Optical(FSO)InterSatellite Link(ISL).However,the challenges posed by the mega LEO satellite constellations,such as limited onboard resources,high-speed movement and the vibration of satellite platforms,present significant obstacles for the existing Pointing,Acquisition and Tracking(PAT)schemes of FSOISL.To address these challenges,we propose a beaconless PAT scheme under satellite platform vibrations,employing a composite scanning approach combining an inner Archimedean spiral scan with an outer regular hexagon step scan.The proposed composite scanning approach covers a wide range of the Field of Uncertainty(FOU)and reduces the required scans by actuator,which can ensure a high Acquisition Probability(AP)while reducing the Average Acquisition Time(AAT)for the inner scan.Specifically,we model and analyze the effect of satellite platform vibrations on the acquisition performance of our beaconless PAT scheme,and derive closed-form expressions for both AP and AAT by utilizing a 2-track model where the acquisition happens on two adjacent spiral scan tracks.By utilizing the theoretical derivations,we can achieve a minimum AAT under diverse APs by selecting appropriate values of overlapping region and scanning range.Simulation results validate that our optimized composite scanning approach for beaconless PAT scheme outperforms the existing schemes.展开更多
The semi-rigid pile-supported composite foundation is widely used in highway projects due to its effectiveness in increasing the bearing capacity and stability of foundations.It is crucial to understand the stress dis...The semi-rigid pile-supported composite foundation is widely used in highway projects due to its effectiveness in increasing the bearing capacity and stability of foundations.It is crucial to understand the stress distribution across the embankment width and the behaviour of unreinforced foundations.Thus,five centrifuge tests were conducted to examine the bearing and deformation behaviours of NPRS(Non-Connected Piled Raft Systems)and GRPS(GeosyntheticReinforced Pile-Supported systems)with varying substratum stiffness,then a comparative analysis was conducted on embankment settlement,pressures underneath the embankments,and axial forces along the piles.The results indicated that greater substratum stiffness correlates with reduced settlement and deformation at various depths.Deformation occurring 5 meters from the embankment toe includes settlement in NPRS and upward movement in GRPS.The potential sliding surface is primarily located within the embankment in NPRS,whereas it may extend through both the embankment and foundation in GRPS.The pile-soil stress ratio and efficiency in NPRS are higher than in GRPS across the embankment.The axial force borne by end-bearing piles is significantly greater than that by floating piles.As the buried depth increases,the axial force in GRPS initially rises then declines,whereas in NPRS,it remains relatively constant within a certain range before decreasing.This study aids in assessing the applicability of composite foundations in complex railway environments and provides a reference for procedural measures under similar conditions.展开更多
With the rapid development of large-scale development of marginal oilfields in China,simple wellhead platforms that are simple in structure and easy to install have become an inevitable choice in the process of oilfie...With the rapid development of large-scale development of marginal oilfields in China,simple wellhead platforms that are simple in structure and easy to install have become an inevitable choice in the process of oilfield development.However,traditional simple wellhead platforms are often discarded after a single use.In pursuit of a more costeffective approach to developing marginal oilfields,this paper proposes a new offshore oil field development facility—an integrated bucket foundation for wellhead platform.To verify the safety of its towing behavior and obtain the dynamic response characteristics of the structure,this paper takes a bucket integrated bucket foundation for wellhead platform with a diameter of 40 m as the research object.By combining physical model tests and numerical simulations,it analyzes the static stability and dynamic response characteristics of the structure during towing,complete with the effects of the draft,wave height,wave period,and towing point height,which produce the dynamic responses of the structure under different influence factors,such as roll angle,pitch angle,heave acceleration and towing force as well as the sensibility to transport variables.The results show that the integrated bucket foundation for wellhead platform is capable of self-floating towing,and its movement is affected by the local environment,which will provide a reference for actual projects.展开更多
Landscape designers increasingly prefer to use wood/bamboo-based composites for outdoor hydrophilic platforms owing to their natural surface texture,high performance,and sustainability to facilitate extensive interact...Landscape designers increasingly prefer to use wood/bamboo-based composites for outdoor hydrophilic platforms owing to their natural surface texture,high performance,and sustainability to facilitate extensive interaction between people and water and enable the full range of ecological functions of water resources.In this study,four laminated composite(LC)structures were designed and manufactured using fluffed bamboo and wood veneers.Their surface textures,profile densities,water resistances,and mechanical properties were then evaluated.The type of fluffed veneer of the surface layer determined the texture of the LC surface.The specific structures of fluffed bamboo and wood veneer laminations were found to affect the LC profile density variability,water resistance,and mechanical properties owing to the differences in the strength and interfacial properties of bamboo and wood fibers.Finally,the water resistance and mechanical properties of all four LCs were found to be much higher than the highest level specified in GB/T 20241-2006 for“laminated veneer lumber”and GB/T 30364-2013 for“bamboo scrimber flooring”,indicating that they are promising materials for structures and flooring,particularly for outdoor hydrophilic platforms.展开更多
With ongoing economic,scientific,and technological developments,the electronic devices used in daily lives are developing toward precision and miniaturization,and so the demand for high-precision manufacturing machine...With ongoing economic,scientific,and technological developments,the electronic devices used in daily lives are developing toward precision and miniaturization,and so the demand for high-precision manufacturing machinery is expanding.The most important piece of equipment in modern high-precision manufacturing is the macro-micro motion platform(M3P),which offers high speed,precision,and efficiency and has macro-micro motion coupling characteristics due to its mechanical design and composition of its driving components.Therefore,the design of the control system is crucial for the overall precision of the platform;conventional proportional–integral–derivative control cannot meet the system requirements,and so M3Ps are the subject of a growing range of modern control strategies.This paper begins by describing the development history of M3Ps,followed by their platform structure and motion control system components,and then in-depth assessments of the macro,micro,and macro-micro control systems.In addition to examining the advantages and disadvantages of current macro-micro motion control,recent technological breakthroughs are noted.Finally,based on existing problems,future directions for M3P control systems are given,and the present conclusions offer guidelines for future work on M3Ps.展开更多
In this paper,the adaptive tracking control problem for macro-micro composite positioning stage(MMCPS)with error constraints and input saturation is considered.The MMCPS has important applications in realizing high-sp...In this paper,the adaptive tracking control problem for macro-micro composite positioning stage(MMCPS)with error constraints and input saturation is considered.The MMCPS has important applications in realizing high-speed macromotion and high-precision micromotion,which can be regarded as a non-strict feedback interconnected nonlinear system.A fixed-time prescribed performance(FTPP)function is proposed to restrict the tracking error and virtual errors.Based on the designed barrier Lyapunov function,the transform errors can also be constrainted in the prescribed constant bounds.Furthermore,an auxiliary system is constructed to compensate adverse effect of the saturation nonlinearity.By integrating the nonlinear filtering technique into the backstepping control framework,the problem of computational complexity explosion can be effectively avoided.For the purpose of achieving better transient performance and improving control precision,an adaptive FTPP tracking control method is presented.According to the Lyapunov stability theory,the proposed control method guarantees that all dynamic errors can converge to the prescribed bounds within fixed time.Finally,a simulation example is given to indicate the effectiveness of the designed controller.展开更多
The testing on the bearing strength of single-shear bolt jointed composite laminates structure is done.And the effect of the fixture on the testing results is analyzed. Then a macro-micro multi-scale analytical model ...The testing on the bearing strength of single-shear bolt jointed composite laminates structure is done.And the effect of the fixture on the testing results is analyzed. Then a macro-micro multi-scale analytical model combined with the improved"Generalized Method of Cells( GMC) "is developed,which is used to predict the macro bearing strength and to characterize the micro constitute material failure of the bolt jointed composite laminates structure. Both the contact conditions at the bolt/hole boundary and the contact conditions at the specimen/fixture boundary,progressive damage,and the material properties degradation are all taken account into the analytical model. Thus,the numerical simulation results agree well with the experimental results.Finally,the effect of the fixture on the testing results is characterized. The results show that the incomplete contaction between the fixture and the specimen or the lack of the lateral constraint on the specimen will affect the limited bearing strength and the offset bearing strength of the bolt jointed composite laminates structure. In addition,the lower support rigid of the fixture will affect the rigid of the bolt jointed composite laminates structure.展开更多
Metazoan fossils in the Gaojiashan Biota are famous for being well preserved and may provide new insights into the early evolution and skeletonization of Metazoans. We are studying the isotopic compositions of organic...Metazoan fossils in the Gaojiashan Biota are famous for being well preserved and may provide new insights into the early evolution and skeletonization of Metazoans. We are studying the isotopic compositions of organic and carbonate carbon from a sequence of sedimentary rocks at the Gaojiashan section, northern Yangtze Platform, Shaanxi Province of China. Organic carbon isotope values display a range between -30.8%0 and -24.7%0 with clear stratigraphic variations. Carbonate carbon isotope data vary between 0.1%o and ＋6%0. Positive j13C values from sediments with Gaojiashan biota reflect temporal variations in carbon turnover, i.e. an increasing in photosynthetic carbon fixation followed by an increasing subsequent fractional organic carbon burial, and that related to bio- radiation such as increasing algae, bacteria, and original creatures productivity in biomass. These secular variations are interpreted to reflect perturbations of the regional carbon cycle, specifically changes in the fractional burial of organic carbon, and discuss the relationship between Gaojiashan biota and paleoenvrionmental variation.展开更多
Ocean platforms are subjected to a variety of environment loads, such as those from winds, waves, currents, etc. In this study, the torsion problems of a gravity platform column with cracks under wind load were invest...Ocean platforms are subjected to a variety of environment loads, such as those from winds, waves, currents, etc. In this study, the torsion problems of a gravity platform column with cracks under wind load were investigated. The colmnn was assumed to be a composite cylinder. Therefore the torsion fracture problem of a composite cylinder was considered, and new boundary integral equations for the Saint-Venant torsion problem of a composite cylinder with curvilinear cracks were derived. The problem was re- duced to solving the boundary integral equations on every boundary. By using the new boundary element method, the torsion prob- lem of the gravity platform colunm with a straight crack under various wind loads was calculated. The obtained results were com- pared with those obtained for a torsion problem of the same column without cracks to prove the applicability of the present method. The comparison showed that the detrimental effect of cracks in a column should be considered in marine engineering.展开更多
基金supported in part by the Major Key Project of PCL of China(No.PCL2024A01)in part by the National Natural Science Foundation of China(Nos.62071141,62027802)+1 种基金in part by the Shenzhen Science and Technology Program of China(Nos.JCYJ20241202123904007,GXWD20231127123203001,JSGG20220831110801003)in part by the Fundamental Research Funds for the Central Universities of China(No.HIT.OCEF.2024046)。
文摘Mega Low Earth Orbit(LEO)satellite constellations can provide pervasive intelligent services in the forthcoming Six-Generation(6G)network via the Free-Space Optical(FSO)InterSatellite Link(ISL).However,the challenges posed by the mega LEO satellite constellations,such as limited onboard resources,high-speed movement and the vibration of satellite platforms,present significant obstacles for the existing Pointing,Acquisition and Tracking(PAT)schemes of FSOISL.To address these challenges,we propose a beaconless PAT scheme under satellite platform vibrations,employing a composite scanning approach combining an inner Archimedean spiral scan with an outer regular hexagon step scan.The proposed composite scanning approach covers a wide range of the Field of Uncertainty(FOU)and reduces the required scans by actuator,which can ensure a high Acquisition Probability(AP)while reducing the Average Acquisition Time(AAT)for the inner scan.Specifically,we model and analyze the effect of satellite platform vibrations on the acquisition performance of our beaconless PAT scheme,and derive closed-form expressions for both AP and AAT by utilizing a 2-track model where the acquisition happens on two adjacent spiral scan tracks.By utilizing the theoretical derivations,we can achieve a minimum AAT under diverse APs by selecting appropriate values of overlapping region and scanning range.Simulation results validate that our optimized composite scanning approach for beaconless PAT scheme outperforms the existing schemes.
基金financially supported by the National Natural Science Foundation of China(Nos.51878577 and 52378463)the Natural Science Foundation of Shandong Provincial,China(No.ZR2022ME042)the School-Enterprise Cooperation Program of China Railway 14th Bureau Group Co.(QTHT-HGLCHSD-00052)。
文摘The semi-rigid pile-supported composite foundation is widely used in highway projects due to its effectiveness in increasing the bearing capacity and stability of foundations.It is crucial to understand the stress distribution across the embankment width and the behaviour of unreinforced foundations.Thus,five centrifuge tests were conducted to examine the bearing and deformation behaviours of NPRS(Non-Connected Piled Raft Systems)and GRPS(GeosyntheticReinforced Pile-Supported systems)with varying substratum stiffness,then a comparative analysis was conducted on embankment settlement,pressures underneath the embankments,and axial forces along the piles.The results indicated that greater substratum stiffness correlates with reduced settlement and deformation at various depths.Deformation occurring 5 meters from the embankment toe includes settlement in NPRS and upward movement in GRPS.The potential sliding surface is primarily located within the embankment in NPRS,whereas it may extend through both the embankment and foundation in GRPS.The pile-soil stress ratio and efficiency in NPRS are higher than in GRPS across the embankment.The axial force borne by end-bearing piles is significantly greater than that by floating piles.As the buried depth increases,the axial force in GRPS initially rises then declines,whereas in NPRS,it remains relatively constant within a certain range before decreasing.This study aids in assessing the applicability of composite foundations in complex railway environments and provides a reference for procedural measures under similar conditions.
基金supported by the National Natural Science Foundation of China(Grant No.52271287).
文摘With the rapid development of large-scale development of marginal oilfields in China,simple wellhead platforms that are simple in structure and easy to install have become an inevitable choice in the process of oilfield development.However,traditional simple wellhead platforms are often discarded after a single use.In pursuit of a more costeffective approach to developing marginal oilfields,this paper proposes a new offshore oil field development facility—an integrated bucket foundation for wellhead platform.To verify the safety of its towing behavior and obtain the dynamic response characteristics of the structure,this paper takes a bucket integrated bucket foundation for wellhead platform with a diameter of 40 m as the research object.By combining physical model tests and numerical simulations,it analyzes the static stability and dynamic response characteristics of the structure during towing,complete with the effects of the draft,wave height,wave period,and towing point height,which produce the dynamic responses of the structure under different influence factors,such as roll angle,pitch angle,heave acceleration and towing force as well as the sensibility to transport variables.The results show that the integrated bucket foundation for wellhead platform is capable of self-floating towing,and its movement is affected by the local environment,which will provide a reference for actual projects.
基金the Science and Technology Project of Zhejiang Province(2021C02012)the Science Foundation of Zhejiang Provincial Department of Education(113429A4F21070)the Science Foundation of Zhejiang Sci-Tech University(11340031282014 and 11343132612052).
文摘Landscape designers increasingly prefer to use wood/bamboo-based composites for outdoor hydrophilic platforms owing to their natural surface texture,high performance,and sustainability to facilitate extensive interaction between people and water and enable the full range of ecological functions of water resources.In this study,four laminated composite(LC)structures were designed and manufactured using fluffed bamboo and wood veneers.Their surface textures,profile densities,water resistances,and mechanical properties were then evaluated.The type of fluffed veneer of the surface layer determined the texture of the LC surface.The specific structures of fluffed bamboo and wood veneer laminations were found to affect the LC profile density variability,water resistance,and mechanical properties owing to the differences in the strength and interfacial properties of bamboo and wood fibers.Finally,the water resistance and mechanical properties of all four LCs were found to be much higher than the highest level specified in GB/T 20241-2006 for“laminated veneer lumber”and GB/T 30364-2013 for“bamboo scrimber flooring”,indicating that they are promising materials for structures and flooring,particularly for outdoor hydrophilic platforms.
基金This research was supported financially by the China Postdoctoral Science Foundation,the National Natural Science Foundation of China(Grant No.51705132)the Young Backbone Teacher Training Program in Henan University of Technology,the Education Department of Henan Province Natural Science Project(Grant No.21A460006)the Natural Science Project of Henan Provincial Department of Science and Technology(Grant No.222102220088).
文摘With ongoing economic,scientific,and technological developments,the electronic devices used in daily lives are developing toward precision and miniaturization,and so the demand for high-precision manufacturing machinery is expanding.The most important piece of equipment in modern high-precision manufacturing is the macro-micro motion platform(M3P),which offers high speed,precision,and efficiency and has macro-micro motion coupling characteristics due to its mechanical design and composition of its driving components.Therefore,the design of the control system is crucial for the overall precision of the platform;conventional proportional–integral–derivative control cannot meet the system requirements,and so M3Ps are the subject of a growing range of modern control strategies.This paper begins by describing the development history of M3Ps,followed by their platform structure and motion control system components,and then in-depth assessments of the macro,micro,and macro-micro control systems.In addition to examining the advantages and disadvantages of current macro-micro motion control,recent technological breakthroughs are noted.Finally,based on existing problems,future directions for M3P control systems are given,and the present conclusions offer guidelines for future work on M3Ps.
基金supported by the National Natural Science Foundation of China(Grant Nos.62403143,52475435,52305456)the National Key Research and Development Program of China(Grant No.2024YFB4610700)+2 种基金the Guangdong Basic and Applied Basic Research Foundation(Grant Nos.2025A1515011789,2025A1515010143,2023A1515010855)the China Postdoctoral Science Foundation(Grant Nos.2025T180472,2024M750576,2024M760581)the Postdoctoral Fellowship Program(Grade C)of China Postdoctoral Science Foundation(Grant Nos.GZC20240312,GZC20230569)。
文摘In this paper,the adaptive tracking control problem for macro-micro composite positioning stage(MMCPS)with error constraints and input saturation is considered.The MMCPS has important applications in realizing high-speed macromotion and high-precision micromotion,which can be regarded as a non-strict feedback interconnected nonlinear system.A fixed-time prescribed performance(FTPP)function is proposed to restrict the tracking error and virtual errors.Based on the designed barrier Lyapunov function,the transform errors can also be constrainted in the prescribed constant bounds.Furthermore,an auxiliary system is constructed to compensate adverse effect of the saturation nonlinearity.By integrating the nonlinear filtering technique into the backstepping control framework,the problem of computational complexity explosion can be effectively avoided.For the purpose of achieving better transient performance and improving control precision,an adaptive FTPP tracking control method is presented.According to the Lyapunov stability theory,the proposed control method guarantees that all dynamic errors can converge to the prescribed bounds within fixed time.Finally,a simulation example is given to indicate the effectiveness of the designed controller.
基金Sponsored by the National Natural Science Foundation of China(Grant No.11272105)the Heilongjiang Province Science Foundation for Youths(Grant No.QC2015003)the Harbin Science and Technology Bureau Young Talent Reserve Project(Grant No.RC2016QN001011,RC2016QN017023)
文摘The testing on the bearing strength of single-shear bolt jointed composite laminates structure is done.And the effect of the fixture on the testing results is analyzed. Then a macro-micro multi-scale analytical model combined with the improved"Generalized Method of Cells( GMC) "is developed,which is used to predict the macro bearing strength and to characterize the micro constitute material failure of the bolt jointed composite laminates structure. Both the contact conditions at the bolt/hole boundary and the contact conditions at the specimen/fixture boundary,progressive damage,and the material properties degradation are all taken account into the analytical model. Thus,the numerical simulation results agree well with the experimental results.Finally,the effect of the fixture on the testing results is characterized. The results show that the incomplete contaction between the fixture and the specimen or the lack of the lateral constraint on the specimen will affect the limited bearing strength and the offset bearing strength of the bolt jointed composite laminates structure. In addition,the lower support rigid of the fixture will affect the rigid of the bolt jointed composite laminates structure.
基金support by the One Hundred Talents Program of the Chinese Academy of Sciencesthe National Natural Science Foundation of China (NSFC Nos. 40972023,40930211, 40902003, 41173008)
文摘Metazoan fossils in the Gaojiashan Biota are famous for being well preserved and may provide new insights into the early evolution and skeletonization of Metazoans. We are studying the isotopic compositions of organic and carbonate carbon from a sequence of sedimentary rocks at the Gaojiashan section, northern Yangtze Platform, Shaanxi Province of China. Organic carbon isotope values display a range between -30.8%0 and -24.7%0 with clear stratigraphic variations. Carbonate carbon isotope data vary between 0.1%o and ＋6%0. Positive j13C values from sediments with Gaojiashan biota reflect temporal variations in carbon turnover, i.e. an increasing in photosynthetic carbon fixation followed by an increasing subsequent fractional organic carbon burial, and that related to bio- radiation such as increasing algae, bacteria, and original creatures productivity in biomass. These secular variations are interpreted to reflect perturbations of the regional carbon cycle, specifically changes in the fractional burial of organic carbon, and discuss the relationship between Gaojiashan biota and paleoenvrionmental variation.
基金supported by the National High-Technology Research and Development Program of China (No.2007AA09Z317)
文摘Ocean platforms are subjected to a variety of environment loads, such as those from winds, waves, currents, etc. In this study, the torsion problems of a gravity platform column with cracks under wind load were investigated. The colmnn was assumed to be a composite cylinder. Therefore the torsion fracture problem of a composite cylinder was considered, and new boundary integral equations for the Saint-Venant torsion problem of a composite cylinder with curvilinear cracks were derived. The problem was re- duced to solving the boundary integral equations on every boundary. By using the new boundary element method, the torsion prob- lem of the gravity platform colunm with a straight crack under various wind loads was calculated. The obtained results were com- pared with those obtained for a torsion problem of the same column without cracks to prove the applicability of the present method. The comparison showed that the detrimental effect of cracks in a column should be considered in marine engineering.
