To accurately control the full-span erection of continuous steel box girder bridges with complex cross-sections and long cantilevers, both the augmented finite element method(A-FEM) and the degenerated plate elements ...To accurately control the full-span erection of continuous steel box girder bridges with complex cross-sections and long cantilevers, both the augmented finite element method(A-FEM) and the degenerated plate elements are adopted in this paper. The entire construction process is simulated by the A-FEM with the mesh-separation-based approximation technique, while the degenerated plate elements are constructed based on 3D isoparametric elements, making it suitable for analysis of a thin-walled structure. This method significantly improves computational efficiency by avoiding numerous degrees of freedom(DoFs) when analyzing complex structures. With characteristics of the full-span erection technology, the end-face angle of adjacent girder segments, the preset distance of girder segments from the design position, and the temperature difference are selected as control parameters, and they are calculated through the structural response of each construction stage. Engineering practice shows that the calculation accuracy of A-FEM is verified by field-measured results. It can be applied rapidly and effectively to evaluate the matching state of girder segments and the stress state of bearings as well as the thermal effect during full-span erection.展开更多
An artificial localized corrosion system is assembled and some parameters related to the localized corrosion in active dissolution state (i.e., non-passive state) have been studied. The results showed that the develop...An artificial localized corrosion system is assembled and some parameters related to the localized corrosion in active dissolution state (i.e., non-passive state) have been studied. The results showed that the developed electrochemical system can satisfactorily imitate a naturally formed localized corrosion and the coupling current can indicate the maximum localized propagating rate. In this artificial system, the anodic dissolution reaction followed the auto-catalytic mechanism. The localized corrosion current density was dependent on the area ratio R of the cathode to the occluded anode. While R was equal to or more than 6, the coupling current reached at a maximum value and did not alter with the increase in R-value. Therefore, R=7 is chosen as one of these optimum parameters used in constructing the system, with which the biggest galvanic current might be obtained. In contrast, the thickness of the polymer filler separating the occluded anode area from the bulk electrolyte solution and the volume of the occluded anode area did not affect the corrosion current obviously. They might affect the response time to approach a steady state.展开更多
The treatment of soft soil foundation under nuclear safety grade corridors with graded sand and gravel materials has a good development prospect.It is of great engineering value to explore the influence of constructio...The treatment of soft soil foundation under nuclear safety grade corridors with graded sand and gravel materials has a good development prospect.It is of great engineering value to explore the influence of construction parameters of graded sand and gravel foundation on the seismic response of gallery structures.Taking the safety grade underground corridor of a nuclear power plant as the engineering background,the equivalent linear method is used to consider the nonlinear dynamic characteristics of graded sand and gravel.The energy transfer boundary is applied at the truncation boundary to simulate the dissipation effect of scattered wave fluctuation energy and the ground motion input.The thicknessless contact element is introduced to consider the contact effect between the corridor structure and the graded sand and gravel foundation,so as to establish the calculation model of the dynamic interaction between the graded sand and gravel foundation and the corridor structure.Furthermore,the influence of the relative compactness and the foundation treatment depth on the seismic response of the corridor structure is studied,and the calculation results of the acceleration response spectrum and relative displacement of the corridor structure are analyzed.The calculation results show that the two construction parameters have different degrees of influence on the seismic response of corridor structure.The research results can provide reference for the engineering design and construction of underground corridors,and provide technical support for the application of graded gravel materials in soft soil foundation treatment.展开更多
Through the systematic analysis of the ground settlement generated by the process of shield tunneling,the relationships between ground deformation and construction parameters are studied in this paper.Based on the ass...Through the systematic analysis of the ground settlement generated by the process of shield tunneling,the relationships between ground deformation and construction parameters are studied in this paper.Based on the assumption of linear small deformation,a mathematical model of the relationship between ground deformation and construction parameters is set up.The principle and method of optimization for estimating ground deformation is studied.The actual measured data are compared with the results of theoretical analysis in a case.Considering different ground formations in different construction sites with different adverse effects on surface and underground structures,the ground surface deformations caused by shield tunneling is an aimed topic in this paper.The contributions and research implications are the revealed relationships between the ground deformation and the shield tunneling parameters during construction.展开更多
For a tunnel driven by a shield machine,the posture of the driving machine is essential to the construction quality and environmental impact.However,the machine posture is controlled by the experienced driver of shiel...For a tunnel driven by a shield machine,the posture of the driving machine is essential to the construction quality and environmental impact.However,the machine posture is controlled by the experienced driver of shield machine by setting hundreds of tunneling parameters empirically.Machine learning(ML)algorithm is an alternative method that can let the computer to learn from the driver’s operation and try to model the relationship between parameters automatically.Thus,in this paper,three ML algorithms,i.e.multi-layer perception(MLP),support vector machine(SVM)and gradient boosting regression(GBR),are improved by genetic algorithm(GA)and principal component analysis(PCA)to predict the tunneling posture of the shield machine.A set of the parameters for shield tunneling is extracted from the construction site of a Shanghai metro.In total,53,785 pairwise data points are collected for about 373 d and the ratio between training set,validation set and test set is 3:1:1.Each pairwise data point includes 83 types of parameters covering the shield posture,construction parameters,and soil stratum properties at the same time.The test results show that the averaged R2 of MLP,SVM and GBR based models are 0.942,0.935 and 0.6,respectively.Then the automatic control for the posture of shield tunnel is illustrated with an application example of the proposed models.The proposed method is proved to be helpful in controlling the construction quality with optimized construction parameters.展开更多
Using the visualized experimental device of temporary plugging in hydraulic fractures, the plugging behaviors of temporary plugging particles with different sizes and concentrations in hydraulic fractures were experim...Using the visualized experimental device of temporary plugging in hydraulic fractures, the plugging behaviors of temporary plugging particles with different sizes and concentrations in hydraulic fractures were experimentally analyzed under the conditions of different carrier fluid displacements and viscosities. The results show that the greater the carrier fluid viscosity and displacement, the more difficult it is to form a plugging layer, and that the larger the size and concentration of the temporary plugging particle, the less difficult it is to form a plugging layer. When the ratio of particle size to fracture width is 0.45, the formation of the plugging layer is mainly controlled by the mass concentration of the temporary plugging particle and the viscosity of the carrier fluid, and a stable plugging layer cannot form if the mass concentration of the temporary plugging particle is less than 20 kg/m^(3)or the viscosity of the carrier fluid is greater than 3 mPa·s. When the ratio of particle size to fracture width is 0.60, the formation of the plugging layer is mainly controlled by the mass concentration of the temporary plugging particle, and a stable plugging layer cannot form if the mass concentration of the temporary plugging particle is less than 10 kg/m^(3). When the ratio of particle size to fracture width is 0.75, the formation of the plugging layer is basically not affected by other parameters, and a stable plugging layer can form within the experimental conditions. The formation process of plugging layer includes two stages and four modes. The main controlling factors affecting the formation mode are the ratio of particle size to fracture width, carrier fluid displacement and carrier fluid viscosity.展开更多
In the core process of fractured marine gas hydrate(hereinafter referred to as hydrate)particles being transported up to the surface platform by airtight pipeline in the solid fluidization exploitation of marine gas h...In the core process of fractured marine gas hydrate(hereinafter referred to as hydrate)particles being transported up to the surface platform by airtight pipeline in the solid fluidization exploitation of marine gas hydrate reservoirs,influenced by the rising temperature and the dropping pressure,the solid hydrates will decompose and produce a large amount of gas at a certain critical point,causing the liquidesolid two-phase flow in the wellbore to change into complicated gaseliquidesolid multiphase non-equilibrium flow,which further aggravate well control,solid phase transportation and other safety risks.In view of this,the dynamic hydrate decomposition law in the above process was studied in this paper by establishing multiphase wellbore flow mathematical models of wellbore temperature and pressure field,hydrate phase equilibrium,hydrate dynamic decomposition in multiphase riser pipe flow,wellbore multiphase flow coupled hydrate dynamic decomposition,and a numerical calculation method was proposed and verified.The following results were obtained.First,by numerical model analysis,the effects of liquid phase displacement,solid throughput(daily gas production rate)and wellhead back pressure under different construction parameters on multi-phase non-equilibrium pipe flow were obtained.In addition,the field construction guidance measures were put forward based on multiphase non-equilibrium pipe flow characteristics as follows:to properly increase the solid throughput so as to increase the natural gas production,to appropriately increase the liquid-phase displacement and the wellhead back pressure so as to ensure well control safety.This study provides not only a theoretical basis for the prediction of multiphase non-equilibrium pipe flow in the solid fluidization exploitation,but a technical support for the field construction parameter optimization and well control safety.展开更多
Hydraulic fracturing of low-permeability continental reservoirs that possess argillaceous interlayers between single sand bodies is poorly understood.In this study,the delta-front-facies,low-permeability sandemudstone...Hydraulic fracturing of low-permeability continental reservoirs that possess argillaceous interlayers between single sand bodies is poorly understood.In this study,the delta-front-facies,low-permeability sandemudstone interbedded reservoir of the Ansai district,Ordos Basin,is used as a case study.The reservoir characteristics of different sedimentary microfacies were identified using information from outcrops,drill cores and well logging.Six reservoir physical models of sandemudstone assemblages were established on the basis of these data.The fracture growth patterns and parameters of the six models were obtained by numerical simulation.Numerical simulation with different fracturing parameters was conducted,to obtain the best parameters for each model to achieve different fracturing effects.The results show that crack size is influenced by the thickness of sandstone and mudstone units,the sandstone to mudstone ratio,and fracturing operation parameters.Sandstone thickness is extremely important in crack propagation.For medium and thick sandstone(3e5 m thick)interbedded with thin mudstone(<0.3 m thick),fracture width and length are large,and longitudinal fractures can pierce mudstone layers.In contrast,for thin sandstone(<1.5 m thick)interbedded with thick mudstone(>0.8 m thick),fractures are small and often restricted to a single sand body,and the mudstone interlayers limit the longitudinal extent of cracks.The six models represent three sedimentary microfacies with different distributions of sandstone and mudstone.Oil well artificial fracture shapes and parameters in different microfacies were visualized through simulation with different models,and match well with data from actual fields We also conducted fracture simulation by changing the fracturing construction parameters to obtain the optimal parameters for different fracturing effects in the models,providing a new understanding of the mudstone interlayers between single sand bodies(>0.3 m thick)and an important basis for oil field construction.展开更多
Electromagnetic(EM)metamaterials represent a cutting-edge field that achieves anomalously macroscopic properties through artificial design and arrangement of microstructure arrays to freely manipulate EM fields and wa...Electromagnetic(EM)metamaterials represent a cutting-edge field that achieves anomalously macroscopic properties through artificial design and arrangement of microstructure arrays to freely manipulate EM fields and waves in desired ways.The unit cell of a microstructure array is also called a meta-atom,which can construct effective medium parameters that do not exist in traditional materials or are difficult to realize with traditional technologies.By deep integration with digital information,the meta-atom is evolved to a digital meta-atom,leading to the emergence of information metamaterials.Information metamaterials break the inherent barriers between the EM and digital domains,providing a physical platform for controlling EM waves and modulating digital information simultaneously.The concepts of meta-atoms and metamaterials are also introduced to high-frequency integrated circuit designs to address issues that cannot be solved by traditional methods,since lumped-parameter models become unsustainable at microscopic scales.By incorporating several meta-atoms to form a metachip,precise manipulation of the EM field distribution can be achieved at microscopic scales.In this perspective,we summarize the physical connotations and main classifications of meta-atoms and briefly discuss their future development trends.Through this article,we hope to draw more research attention to explore the potential values of meta-atoms,thereby opening up a broader stage for the in-depth development of metamaterials.展开更多
基金Project supported by the National Natural Science Foundation of China(Nos.51578496 and 51878603)the Zhejiang Provincial Natural Science Foundation of China(No.LZ16E080001)。
文摘To accurately control the full-span erection of continuous steel box girder bridges with complex cross-sections and long cantilevers, both the augmented finite element method(A-FEM) and the degenerated plate elements are adopted in this paper. The entire construction process is simulated by the A-FEM with the mesh-separation-based approximation technique, while the degenerated plate elements are constructed based on 3D isoparametric elements, making it suitable for analysis of a thin-walled structure. This method significantly improves computational efficiency by avoiding numerous degrees of freedom(DoFs) when analyzing complex structures. With characteristics of the full-span erection technology, the end-face angle of adjacent girder segments, the preset distance of girder segments from the design position, and the temperature difference are selected as control parameters, and they are calculated through the structural response of each construction stage. Engineering practice shows that the calculation accuracy of A-FEM is verified by field-measured results. It can be applied rapidly and effectively to evaluate the matching state of girder segments and the stress state of bearings as well as the thermal effect during full-span erection.
文摘An artificial localized corrosion system is assembled and some parameters related to the localized corrosion in active dissolution state (i.e., non-passive state) have been studied. The results showed that the developed electrochemical system can satisfactorily imitate a naturally formed localized corrosion and the coupling current can indicate the maximum localized propagating rate. In this artificial system, the anodic dissolution reaction followed the auto-catalytic mechanism. The localized corrosion current density was dependent on the area ratio R of the cathode to the occluded anode. While R was equal to or more than 6, the coupling current reached at a maximum value and did not alter with the increase in R-value. Therefore, R=7 is chosen as one of these optimum parameters used in constructing the system, with which the biggest galvanic current might be obtained. In contrast, the thickness of the polymer filler separating the occluded anode area from the bulk electrolyte solution and the volume of the occluded anode area did not affect the corrosion current obviously. They might affect the response time to approach a steady state.
基金supported by National Natural Science Foundation of China(52108437)Dalian Youth Science and Technology Star Project(2020RQ057)。
文摘The treatment of soft soil foundation under nuclear safety grade corridors with graded sand and gravel materials has a good development prospect.It is of great engineering value to explore the influence of construction parameters of graded sand and gravel foundation on the seismic response of gallery structures.Taking the safety grade underground corridor of a nuclear power plant as the engineering background,the equivalent linear method is used to consider the nonlinear dynamic characteristics of graded sand and gravel.The energy transfer boundary is applied at the truncation boundary to simulate the dissipation effect of scattered wave fluctuation energy and the ground motion input.The thicknessless contact element is introduced to consider the contact effect between the corridor structure and the graded sand and gravel foundation,so as to establish the calculation model of the dynamic interaction between the graded sand and gravel foundation and the corridor structure.Furthermore,the influence of the relative compactness and the foundation treatment depth on the seismic response of the corridor structure is studied,and the calculation results of the acceleration response spectrum and relative displacement of the corridor structure are analyzed.The calculation results show that the two construction parameters have different degrees of influence on the seismic response of corridor structure.The research results can provide reference for the engineering design and construction of underground corridors,and provide technical support for the application of graded gravel materials in soft soil foundation treatment.
文摘Through the systematic analysis of the ground settlement generated by the process of shield tunneling,the relationships between ground deformation and construction parameters are studied in this paper.Based on the assumption of linear small deformation,a mathematical model of the relationship between ground deformation and construction parameters is set up.The principle and method of optimization for estimating ground deformation is studied.The actual measured data are compared with the results of theoretical analysis in a case.Considering different ground formations in different construction sites with different adverse effects on surface and underground structures,the ground surface deformations caused by shield tunneling is an aimed topic in this paper.The contributions and research implications are the revealed relationships between the ground deformation and the shield tunneling parameters during construction.
基金supported by the National Natural Science Foundation of China(Grant Nos.52130805 and 51978516)Scientific Program of Shanghai Science and Technology Committee(Grant No.20dz1202200).
文摘For a tunnel driven by a shield machine,the posture of the driving machine is essential to the construction quality and environmental impact.However,the machine posture is controlled by the experienced driver of shield machine by setting hundreds of tunneling parameters empirically.Machine learning(ML)algorithm is an alternative method that can let the computer to learn from the driver’s operation and try to model the relationship between parameters automatically.Thus,in this paper,three ML algorithms,i.e.multi-layer perception(MLP),support vector machine(SVM)and gradient boosting regression(GBR),are improved by genetic algorithm(GA)and principal component analysis(PCA)to predict the tunneling posture of the shield machine.A set of the parameters for shield tunneling is extracted from the construction site of a Shanghai metro.In total,53,785 pairwise data points are collected for about 373 d and the ratio between training set,validation set and test set is 3:1:1.Each pairwise data point includes 83 types of parameters covering the shield posture,construction parameters,and soil stratum properties at the same time.The test results show that the averaged R2 of MLP,SVM and GBR based models are 0.942,0.935 and 0.6,respectively.Then the automatic control for the posture of shield tunnel is illustrated with an application example of the proposed models.The proposed method is proved to be helpful in controlling the construction quality with optimized construction parameters.
基金Supported by National Natural Science Foundation of China (U21A20105)Science and Technology Innovation Fund of PetroChina (2020D-5007-0208)。
文摘Using the visualized experimental device of temporary plugging in hydraulic fractures, the plugging behaviors of temporary plugging particles with different sizes and concentrations in hydraulic fractures were experimentally analyzed under the conditions of different carrier fluid displacements and viscosities. The results show that the greater the carrier fluid viscosity and displacement, the more difficult it is to form a plugging layer, and that the larger the size and concentration of the temporary plugging particle, the less difficult it is to form a plugging layer. When the ratio of particle size to fracture width is 0.45, the formation of the plugging layer is mainly controlled by the mass concentration of the temporary plugging particle and the viscosity of the carrier fluid, and a stable plugging layer cannot form if the mass concentration of the temporary plugging particle is less than 20 kg/m^(3)or the viscosity of the carrier fluid is greater than 3 mPa·s. When the ratio of particle size to fracture width is 0.60, the formation of the plugging layer is mainly controlled by the mass concentration of the temporary plugging particle, and a stable plugging layer cannot form if the mass concentration of the temporary plugging particle is less than 10 kg/m^(3). When the ratio of particle size to fracture width is 0.75, the formation of the plugging layer is basically not affected by other parameters, and a stable plugging layer can form within the experimental conditions. The formation process of plugging layer includes two stages and four modes. The main controlling factors affecting the formation mode are the ratio of particle size to fracture width, carrier fluid displacement and carrier fluid viscosity.
基金Project supported by the National Key R&D Program“New Technology for Marine Hydrate Solid Fluidization Testing”(No.:2016YFC0304008)Strategic Research Project for Medium-and Long-Term Development Strategy Research in China's Engineering Science and Technology“Research on Deep Sea Gas Hydrate Development Strategy for 2035”(No.:2017-ZCQ-5)Key Project of National Natural Science Foundation of China,and“Measurement and Control Theory and Key Issues of Managed Pressure Drilling”(No.:51334003).
文摘In the core process of fractured marine gas hydrate(hereinafter referred to as hydrate)particles being transported up to the surface platform by airtight pipeline in the solid fluidization exploitation of marine gas hydrate reservoirs,influenced by the rising temperature and the dropping pressure,the solid hydrates will decompose and produce a large amount of gas at a certain critical point,causing the liquidesolid two-phase flow in the wellbore to change into complicated gaseliquidesolid multiphase non-equilibrium flow,which further aggravate well control,solid phase transportation and other safety risks.In view of this,the dynamic hydrate decomposition law in the above process was studied in this paper by establishing multiphase wellbore flow mathematical models of wellbore temperature and pressure field,hydrate phase equilibrium,hydrate dynamic decomposition in multiphase riser pipe flow,wellbore multiphase flow coupled hydrate dynamic decomposition,and a numerical calculation method was proposed and verified.The following results were obtained.First,by numerical model analysis,the effects of liquid phase displacement,solid throughput(daily gas production rate)and wellhead back pressure under different construction parameters on multi-phase non-equilibrium pipe flow were obtained.In addition,the field construction guidance measures were put forward based on multiphase non-equilibrium pipe flow characteristics as follows:to properly increase the solid throughput so as to increase the natural gas production,to appropriately increase the liquid-phase displacement and the wellhead back pressure so as to ensure well control safety.This study provides not only a theoretical basis for the prediction of multiphase non-equilibrium pipe flow in the solid fluidization exploitation,but a technical support for the field construction parameter optimization and well control safety.
文摘Hydraulic fracturing of low-permeability continental reservoirs that possess argillaceous interlayers between single sand bodies is poorly understood.In this study,the delta-front-facies,low-permeability sandemudstone interbedded reservoir of the Ansai district,Ordos Basin,is used as a case study.The reservoir characteristics of different sedimentary microfacies were identified using information from outcrops,drill cores and well logging.Six reservoir physical models of sandemudstone assemblages were established on the basis of these data.The fracture growth patterns and parameters of the six models were obtained by numerical simulation.Numerical simulation with different fracturing parameters was conducted,to obtain the best parameters for each model to achieve different fracturing effects.The results show that crack size is influenced by the thickness of sandstone and mudstone units,the sandstone to mudstone ratio,and fracturing operation parameters.Sandstone thickness is extremely important in crack propagation.For medium and thick sandstone(3e5 m thick)interbedded with thin mudstone(<0.3 m thick),fracture width and length are large,and longitudinal fractures can pierce mudstone layers.In contrast,for thin sandstone(<1.5 m thick)interbedded with thick mudstone(>0.8 m thick),fractures are small and often restricted to a single sand body,and the mudstone interlayers limit the longitudinal extent of cracks.The six models represent three sedimentary microfacies with different distributions of sandstone and mudstone.Oil well artificial fracture shapes and parameters in different microfacies were visualized through simulation with different models,and match well with data from actual fields We also conducted fracture simulation by changing the fracturing construction parameters to obtain the optimal parameters for different fracturing effects in the models,providing a new understanding of the mudstone interlayers between single sand bodies(>0.3 m thick)and an important basis for oil field construction.
基金supported by the Project on Frontier and Interdisciplinary Research Assessment,Academic Divisions of the Chinese Academy of Sciences(Grant No.XK2023XXA001)the National Natural Science Foundation of China(Grant Nos.62422106,62131007,62471109,and 62288101).
文摘Electromagnetic(EM)metamaterials represent a cutting-edge field that achieves anomalously macroscopic properties through artificial design and arrangement of microstructure arrays to freely manipulate EM fields and waves in desired ways.The unit cell of a microstructure array is also called a meta-atom,which can construct effective medium parameters that do not exist in traditional materials or are difficult to realize with traditional technologies.By deep integration with digital information,the meta-atom is evolved to a digital meta-atom,leading to the emergence of information metamaterials.Information metamaterials break the inherent barriers between the EM and digital domains,providing a physical platform for controlling EM waves and modulating digital information simultaneously.The concepts of meta-atoms and metamaterials are also introduced to high-frequency integrated circuit designs to address issues that cannot be solved by traditional methods,since lumped-parameter models become unsustainable at microscopic scales.By incorporating several meta-atoms to form a metachip,precise manipulation of the EM field distribution can be achieved at microscopic scales.In this perspective,we summarize the physical connotations and main classifications of meta-atoms and briefly discuss their future development trends.Through this article,we hope to draw more research attention to explore the potential values of meta-atoms,thereby opening up a broader stage for the in-depth development of metamaterials.
