With the development of power system,the operation mode of powersystem is becoming more and more complex.In order to improve the security level of power system operation,a knowledge-driven method for calculating the t...With the development of power system,the operation mode of powersystem is becoming more and more complex.In order to improve the security level of power system operation,a knowledge-driven method for calculating the transmission section limit of large-scale power grid is proposed.Firstly,a calculation model of transmission section limit is established by comprehensively considering static security and stability constraints and transient stability constraints of a large power grid;Then,a knowledge-driven calculation method of transmission section limit is proposed,which makes the calculation process of transmission section limit knowledgeable through knowledge mapping,and the implementation scheme of generator autonomous search and generator optimal switching is designed to realize the fast calculation of transmission section limit of large power grid.Finally,the effectiveness and correctness of the proposed method are verified in a regional power grid with 2128 nodes and a cross-regional power grid with 12643nodes in China.展开更多
A typical airfoil section system with freeplay is investigated in the paper. The classic quasi-steady flow model is applied to calculate the aerodynamics, and a piecewise-stiffness model is adopted to characterize the...A typical airfoil section system with freeplay is investigated in the paper. The classic quasi-steady flow model is applied to calculate the aerodynamics, and a piecewise-stiffness model is adopted to characterize the non- linearity of the airfoil section＇s freeplay. There are two crit- ical speeds in the system, i.e., a lower critical speed, above which the system might generate limit cycle oscillation, and an upper critical one, above which the system will flutter. Then a Poincar6 map is constructed for the limit cycle os- cillations by using piecewise-linear solutions with and with- out contact in the system. Through analysis of the Poincar6 map, a series of equations which can determine the frequen- cies of period-1 limit cycle oscillations at any flight veloc- ity are derived. Finally, these analytic results are compared to the results of numerical simulations, and a good agree- ment is found. The effects of freeplay value and contact stiffness ratio on the limit cycle oscillation are also analyzed through numerical simulations of the original system. More- over, there exist multi-periods limit cycle oscillations and even complicated ＂chaotic＂ oscillations may occur, which are usually found in smooth nonlinear dynamic systems.展开更多
With von Mises yield criterion,the loading range of Net Section Collapse(NSC) Criteria is extended from combined tension and bending loadings to combined bending,torsion and internal pressure loadings.A new theoretica...With von Mises yield criterion,the loading range of Net Section Collapse(NSC) Criteria is extended from combined tension and bending loadings to combined bending,torsion and internal pressure loadings.A new theoretical analyzing method of plastic limit load for pressure pipe with incomplete welding defects based on the extended NSC Criteria is presented and the correlative formulas are deduced,the influences of pipe curvature,circumferential length and depth of incomplete welding defects on the plastic limit load of pressure pipe are considered as well in this method.Meanwhile,according to the orthogonal experimental design method,the plastic limit loads are calculated by the finite element method and compared with the theoretical values.The results show that the expressions of plastic limit load of pressure pipe with incomplete welding defects under bending,torsion and internal pressure based on extended NSC criteria are reliable.The study provides an important theoretical basis for the establishment of safety assessment measure towards pressure pipe with incomplete welding defects.展开更多
目的:探究时限管理策略配合标准化快速反应团体干预对紧急剖宫产母婴结局的影响。方法:选取2020年1月—2022年12月在江苏省盐城市第一人民医院产科进行紧急剖宫产的100例产妇为研究对象,根据实施时限管理策略配合标准化快速反应团体干...目的:探究时限管理策略配合标准化快速反应团体干预对紧急剖宫产母婴结局的影响。方法:选取2020年1月—2022年12月在江苏省盐城市第一人民医院产科进行紧急剖宫产的100例产妇为研究对象,根据实施时限管理策略配合标准化快速反应团体干预时间前后分为对照组与研究组,对照组行常规紧急剖宫产手术,研究组实施以时限管理策略配合标准化快速反应团体干预为基础的紧急剖宫产手术,比较两组手术至胎儿娩出时间(DDI)、手术指标及胎儿结局。结果:干预后,研究组产妇DDI时间及手术时间、术中出血量、止血时间、住院时间均低于对照组,差异有统计学意义(P<0.001);研究组新生儿出生后1 min及5 min Apgar评分高于对照组,差异有统计学意义(P<0.001)。两组窒息发生率比较,差异无统计学意义(P>0.05)。结论:对紧急剖宫产产妇实施基于时限管理策略配合标准化快速反应团体干预,能缩短产妇DDI时间,改善手术相应指标及新生儿结局。展开更多
The ultimate strength of reinforced concrete(RC) rectangular members subjected to combined bending,shear and torsion is obtained from the limit analysis proposed in the present paper. Based on a warped failure surface...The ultimate strength of reinforced concrete(RC) rectangular members subjected to combined bending,shear and torsion is obtained from the limit analysis proposed in the present paper. Based on a warped failure surface determined by external loads, and a reasonable assumed stress distribution balancing external loads but not violating the yield condition, the bending-shear-torsion interaction can be derived from equilibrium conditions.According to the definition of lower-bound theorem in limit analysis, the calculated ultimate loads will be carried safely by the structure. The present method is a simple approach to obtain carrying capacities for RC elements under complex external loads. After comparing with the test results, a good agreement has been observed. The present method can be extended to explain the failure mechanism of RC members subjected to axial loads, and it is possible to develop a simple unified theory of RC members for engineering.展开更多
为探明火灾下活性粉末混凝土(Receative power concrete,RPC)梁斜截面承载性能退化规律,设计制作了六根RPC简支梁试件,开展了恒载下ISO834标准火灾试验,获得了时间-位移曲线、荷载-位移曲线、内部温度变化、裂缝开展、破坏形态、高温爆...为探明火灾下活性粉末混凝土(Receative power concrete,RPC)梁斜截面承载性能退化规律,设计制作了六根RPC简支梁试件,开展了恒载下ISO834标准火灾试验,获得了时间-位移曲线、荷载-位移曲线、内部温度变化、裂缝开展、破坏形态、高温爆裂等数据,分析了剪跨比、荷载水平、配箍率、纵筋配筋率对火灾下RPC梁斜截面承载性能的影响规律。结果表明:剪跨比、荷载水平是影响RPC梁斜截面耐火极限的关键因素,剪跨比由2.5增至3.5,荷载水平由0.25增至0.45,RPC梁耐火极限可降低30 min以上;配箍率对RPC梁的斜截面承载力和耐火极限影响显著;纵筋配筋率对RPC梁耐火极限影响甚微。火灾高温、爆裂削弱了RPC梁的斜截面承载性能,爆裂导致内部材料直接受火,加速其力学性能劣化,使梁斜截面承载力降低33.5%以上。该研究可为火灾下RPC梁斜截面承载安全及火灾后加固修复提供参考。展开更多
基金supported by the Science andTechnology Project of State Grid:Research on artificial intelligence analysis technology of available transmission capacity(ATC)of key section under multiple power grid operation modes(5100-202255020A-1–1-ZN).
文摘With the development of power system,the operation mode of powersystem is becoming more and more complex.In order to improve the security level of power system operation,a knowledge-driven method for calculating the transmission section limit of large-scale power grid is proposed.Firstly,a calculation model of transmission section limit is established by comprehensively considering static security and stability constraints and transient stability constraints of a large power grid;Then,a knowledge-driven calculation method of transmission section limit is proposed,which makes the calculation process of transmission section limit knowledgeable through knowledge mapping,and the implementation scheme of generator autonomous search and generator optimal switching is designed to realize the fast calculation of transmission section limit of large power grid.Finally,the effectiveness and correctness of the proposed method are verified in a regional power grid with 2128 nodes and a cross-regional power grid with 12643nodes in China.
基金supported by the National Science Fund for Distinguished Young Scholars in China(11225212)the Young Teachers' Funds of Hunan Province,China
文摘A typical airfoil section system with freeplay is investigated in the paper. The classic quasi-steady flow model is applied to calculate the aerodynamics, and a piecewise-stiffness model is adopted to characterize the non- linearity of the airfoil section＇s freeplay. There are two crit- ical speeds in the system, i.e., a lower critical speed, above which the system might generate limit cycle oscillation, and an upper critical one, above which the system will flutter. Then a Poincar6 map is constructed for the limit cycle os- cillations by using piecewise-linear solutions with and with- out contact in the system. Through analysis of the Poincar6 map, a series of equations which can determine the frequen- cies of period-1 limit cycle oscillations at any flight veloc- ity are derived. Finally, these analytic results are compared to the results of numerical simulations, and a good agree- ment is found. The effects of freeplay value and contact stiffness ratio on the limit cycle oscillation are also analyzed through numerical simulations of the original system. More- over, there exist multi-periods limit cycle oscillations and even complicated ＂chaotic＂ oscillations may occur, which are usually found in smooth nonlinear dynamic systems.
基金Project (No. X106871) supported by the Natural Science Foundation of Zhejiang Province,China
文摘With von Mises yield criterion,the loading range of Net Section Collapse(NSC) Criteria is extended from combined tension and bending loadings to combined bending,torsion and internal pressure loadings.A new theoretical analyzing method of plastic limit load for pressure pipe with incomplete welding defects based on the extended NSC Criteria is presented and the correlative formulas are deduced,the influences of pipe curvature,circumferential length and depth of incomplete welding defects on the plastic limit load of pressure pipe are considered as well in this method.Meanwhile,according to the orthogonal experimental design method,the plastic limit loads are calculated by the finite element method and compared with the theoretical values.The results show that the expressions of plastic limit load of pressure pipe with incomplete welding defects under bending,torsion and internal pressure based on extended NSC criteria are reliable.The study provides an important theoretical basis for the establishment of safety assessment measure towards pressure pipe with incomplete welding defects.
文摘目的:探究时限管理策略配合标准化快速反应团体干预对紧急剖宫产母婴结局的影响。方法:选取2020年1月—2022年12月在江苏省盐城市第一人民医院产科进行紧急剖宫产的100例产妇为研究对象,根据实施时限管理策略配合标准化快速反应团体干预时间前后分为对照组与研究组,对照组行常规紧急剖宫产手术,研究组实施以时限管理策略配合标准化快速反应团体干预为基础的紧急剖宫产手术,比较两组手术至胎儿娩出时间(DDI)、手术指标及胎儿结局。结果:干预后,研究组产妇DDI时间及手术时间、术中出血量、止血时间、住院时间均低于对照组,差异有统计学意义(P<0.001);研究组新生儿出生后1 min及5 min Apgar评分高于对照组,差异有统计学意义(P<0.001)。两组窒息发生率比较,差异无统计学意义(P>0.05)。结论:对紧急剖宫产产妇实施基于时限管理策略配合标准化快速反应团体干预,能缩短产妇DDI时间,改善手术相应指标及新生儿结局。
基金the National Natural Science Foundation of China(No.51178265)
文摘The ultimate strength of reinforced concrete(RC) rectangular members subjected to combined bending,shear and torsion is obtained from the limit analysis proposed in the present paper. Based on a warped failure surface determined by external loads, and a reasonable assumed stress distribution balancing external loads but not violating the yield condition, the bending-shear-torsion interaction can be derived from equilibrium conditions.According to the definition of lower-bound theorem in limit analysis, the calculated ultimate loads will be carried safely by the structure. The present method is a simple approach to obtain carrying capacities for RC elements under complex external loads. After comparing with the test results, a good agreement has been observed. The present method can be extended to explain the failure mechanism of RC members subjected to axial loads, and it is possible to develop a simple unified theory of RC members for engineering.
文摘为探明火灾下活性粉末混凝土(Receative power concrete,RPC)梁斜截面承载性能退化规律,设计制作了六根RPC简支梁试件,开展了恒载下ISO834标准火灾试验,获得了时间-位移曲线、荷载-位移曲线、内部温度变化、裂缝开展、破坏形态、高温爆裂等数据,分析了剪跨比、荷载水平、配箍率、纵筋配筋率对火灾下RPC梁斜截面承载性能的影响规律。结果表明:剪跨比、荷载水平是影响RPC梁斜截面耐火极限的关键因素,剪跨比由2.5增至3.5,荷载水平由0.25增至0.45,RPC梁耐火极限可降低30 min以上;配箍率对RPC梁的斜截面承载力和耐火极限影响显著;纵筋配筋率对RPC梁耐火极限影响甚微。火灾高温、爆裂削弱了RPC梁的斜截面承载性能,爆裂导致内部材料直接受火,加速其力学性能劣化,使梁斜截面承载力降低33.5%以上。该研究可为火灾下RPC梁斜截面承载安全及火灾后加固修复提供参考。
