Given the background of a transmission tower erected on a particular mining subsidence area,we used finite element modeling to analyze the anti-deformation performance of transmission towers under a number of differen...Given the background of a transmission tower erected on a particular mining subsidence area,we used finite element modeling to analyze the anti-deformation performance of transmission towers under a number of different load conditions,including horizontal foundation displacement,uneven vertical downward displacement,wind loads and icing conditions.The results show that the failure in stability of a single steel angle iron represents the limit of the tower given ground deformation.We calculated the corresponding limits of foundation displacements.The results indicate that compression displacement of the foundation is more dangerous than tension displacement.Under complex foundation displacement conditions,horizontal foundation displacement is a key factor leading to failure in the stability of towers.Under conditions of compression or tension displacement of the foundation,wind load becomes the key factor.Towers do not fail when foundation displacements are smaller than 1% (under tension) or 0.5% (under horizontal compression or single foundation subsidence) of the distance between two supports.展开更多
双芯移相变压器中有载分接开关开断级电压、电流的大小与负载条件关系密切,为了确定负载条件对有载分接开关技术参数的影响,在介绍双芯移相变压器的工作原理及运行特性的基础上,推导了实用、精确的负载条件下的级电压计算式,并以230 k V...双芯移相变压器中有载分接开关开断级电压、电流的大小与负载条件关系密切,为了确定负载条件对有载分接开关技术参数的影响,在介绍双芯移相变压器的工作原理及运行特性的基础上,推导了实用、精确的负载条件下的级电压计算式,并以230 k V/150 MVA双芯移相变压器为例,通过对比计算式与MATLAB/SIMULINK仿真模型的结果,验证了级电压计算式的准确性。通过分析级电压与负载大小及性质的关系表明,采用负载条件下的级电压计算方法可更为准确地确定移相变压器有载分接开关的技术参数。此外,通过分析负载功率因数对最大级电压的影响可知级电压随着负载功率因数的增大而增大。展开更多
In order to well understand the mechanism of the mechanotransduction in bone, we propose a new model of transverse iso- tropic and poroelastic osteon cylinder considering Haversian fluid pressure. The analytical pore ...In order to well understand the mechanism of the mechanotransduction in bone, we propose a new model of transverse iso- tropic and poroelastic osteon cylinder considering Haversian fluid pressure. The analytical pore pressure and velocity solutions are obtained to examine the fluid transport behavior and pressure distribution in a loaded osteon on two different exterior sur- face cases. Case I is stress free and fully permeable and case I1 is impermeable. The following are the results obtained. （i） The Haversian fluid may not be ignored because it can enlarge the whole osteonal fluid pressure field, and it bears the external loads together with the solid skeleton. （ii） The increase of both axial strain amplitude and frequency can result in the increase of fluid pressure and velocity amplitudes, while in case II, the frequency has little effect on the fluid pressure amplitude. （iii） Under the same loading conditions, the pressure amplitude in case II is larger than that in case I, while the velocity amplitude is smaller than that in case I. This model permits the linking of the external loads to the osteonal fluid pressure and velocity, which may be a stimulus to the mechanotransduction of bone remodeling signals.展开更多
电磁波在无线通信等领域的广泛应用导致了严重的电磁污染,迫切需要研发高性能电磁波吸收材料.本文针对吸波材料阻抗不匹配等关键问题,设计并成功制备了新型核壳LaOCl/LaFeO_(3)纳米纤维电磁波吸收剂.这种独特的一维多级结构由导电LaFeO_...电磁波在无线通信等领域的广泛应用导致了严重的电磁污染,迫切需要研发高性能电磁波吸收材料.本文针对吸波材料阻抗不匹配等关键问题,设计并成功制备了新型核壳LaOCl/LaFeO_(3)纳米纤维电磁波吸收剂.这种独特的一维多级结构由导电LaFeO_(3)磁性壳层和离子化合物LaOCl核层组成.基于介电-磁损耗耦合和阻抗匹配的协同作用,LaOCl/LaFeO_(3)纳米纤维在超低负载条件下(4 w t%),表现出-40.1 d B(2.0 mm)的反射损耗和6.4 GHz(2.4 mm)的有效吸收带宽.该工作提出了一种新型LaOCl/LaFeO_(3)纳米纤维吸波材料,并为阻抗匹配调控和电磁吸波性能优化开辟了新策略.展开更多
This paper is to study the two-dimensional stress distribution of a finite functionally graded material (FGM) plate with a circular hole under arbitrary constant loads. Using the method of piece-wise homogeneous layer...This paper is to study the two-dimensional stress distribution of a finite functionally graded material (FGM) plate with a circular hole under arbitrary constant loads. Using the method of piece-wise homogeneous layers, the stress analysis of the finite FGM plate having radial arbitrary elastic properties is made based on the complex variable method combined with the least square boundary collocation technique. Numerical results of stress distribution around the hole are then presented for different loading conditions, different material properties and different plate sizes, respectively. It is shown that the stress concentration in the finite plate is generally enhanced compared with the case of an infinite plate, but it can be significantly reduced by choosing proper change ways of the radial elastic modulus.展开更多
Ductile fracture generally relates to microscopic voiding and to strain localization in metallic materials.When the void size is reduced to the nanoscale,size effects often lead to a different macroscopic plastic beha...Ductile fracture generally relates to microscopic voiding and to strain localization in metallic materials.When the void size is reduced to the nanoscale,size effects often lead to a different macroscopic plastic behavior from that established for the same material with larger voids.For example,irradiation of metallic materials can generate a large number of voids at the nanoscale,leading to complex deformation behaviors.The present work advances the understanding of strain localization in nanoporous metallic materials,connecting both the microscopic(nano-)and macroscopic scales.To explore the physical mechanisms at the nanoscale,molecular dynamics(MD)simulations were here carried out,capturing multiple nanovoids explicitly.Then,a homogenized continuum theory based in Gurson's constitutive framework is proposed,which enables us to explore how localized behavior at the macroscopic scale evolves.The homogenized model incorporates the surface tension associated with nanosized void.The importance of this surface tension is illustrated by several parametric studies on the conditions of localization,when a specimen is subjected to uniaxial tension.Our parametric studies show that for smaller nanovoid sizes,and for a hardening matrix material,shear localization onset is delayed.Our proposed homogenization model was then used to predict localization behavior captured by our MD simulation.The yield stress and the localization strain predicted by our continuum model are in general agreement with the trends obtained by MD simulation.Moreover,based on our present study,experimental results of shear failure strain vs.dose of irradiation for several metals could be qualitatively explained rather successfully.Our model can therefore help shed light on prolonging the operation limits and the lifetime of irradiated metallic materials under complex loading conditions.展开更多
基金National Natural Science Foundation of China(No.50004008)Xuzhou Power Supply Company and the Fundamental Research Funds for the Central Universities(No.2011QNB18) for their financial and technical support for this work
文摘Given the background of a transmission tower erected on a particular mining subsidence area,we used finite element modeling to analyze the anti-deformation performance of transmission towers under a number of different load conditions,including horizontal foundation displacement,uneven vertical downward displacement,wind loads and icing conditions.The results show that the failure in stability of a single steel angle iron represents the limit of the tower given ground deformation.We calculated the corresponding limits of foundation displacements.The results indicate that compression displacement of the foundation is more dangerous than tension displacement.Under complex foundation displacement conditions,horizontal foundation displacement is a key factor leading to failure in the stability of towers.Under conditions of compression or tension displacement of the foundation,wind load becomes the key factor.Towers do not fail when foundation displacements are smaller than 1% (under tension) or 0.5% (under horizontal compression or single foundation subsidence) of the distance between two supports.
文摘双芯移相变压器中有载分接开关开断级电压、电流的大小与负载条件关系密切,为了确定负载条件对有载分接开关技术参数的影响,在介绍双芯移相变压器的工作原理及运行特性的基础上,推导了实用、精确的负载条件下的级电压计算式,并以230 k V/150 MVA双芯移相变压器为例,通过对比计算式与MATLAB/SIMULINK仿真模型的结果,验证了级电压计算式的准确性。通过分析级电压与负载大小及性质的关系表明,采用负载条件下的级电压计算方法可更为准确地确定移相变压器有载分接开关的技术参数。此外,通过分析负载功率因数对最大级电压的影响可知级电压随着负载功率因数的增大而增大。
基金supported by the National Natural Science Foundation ofChina (Grant No. 11032008)the Shanxi Province Outstanding Innovation Project for Graduates (Grant No. 20113041)
文摘In order to well understand the mechanism of the mechanotransduction in bone, we propose a new model of transverse iso- tropic and poroelastic osteon cylinder considering Haversian fluid pressure. The analytical pore pressure and velocity solutions are obtained to examine the fluid transport behavior and pressure distribution in a loaded osteon on two different exterior sur- face cases. Case I is stress free and fully permeable and case I1 is impermeable. The following are the results obtained. （i） The Haversian fluid may not be ignored because it can enlarge the whole osteonal fluid pressure field, and it bears the external loads together with the solid skeleton. （ii） The increase of both axial strain amplitude and frequency can result in the increase of fluid pressure and velocity amplitudes, while in case II, the frequency has little effect on the fluid pressure amplitude. （iii） Under the same loading conditions, the pressure amplitude in case II is larger than that in case I, while the velocity amplitude is smaller than that in case I. This model permits the linking of the external loads to the osteonal fluid pressure and velocity, which may be a stimulus to the mechanotransduction of bone remodeling signals.
基金financially supported by the National Natural Science Foundation of China(52102068,52073156,and 52202058)the State Key Laboratory of New Ceramic and Fine Processing,Tsinghua University(KF202112)+5 种基金the Science and Technology on Advanced Functional Composite Laboratory(6142906200509)the Natural Science Foundation of Jiangsu Province(20KJB430017)NUPTSF(NY219162)the Key Science and Technology Program of Henan Province(212102210591)the Foundation for University Youth Key Teachers of Henan Province(2020GGJS170)the Support Program for Scientific and Technological Innovation Talents of Higher Education in Henan Province(21HASTIT004)。
文摘电磁波在无线通信等领域的广泛应用导致了严重的电磁污染,迫切需要研发高性能电磁波吸收材料.本文针对吸波材料阻抗不匹配等关键问题,设计并成功制备了新型核壳LaOCl/LaFeO_(3)纳米纤维电磁波吸收剂.这种独特的一维多级结构由导电LaFeO_(3)磁性壳层和离子化合物LaOCl核层组成.基于介电-磁损耗耦合和阻抗匹配的协同作用,LaOCl/LaFeO_(3)纳米纤维在超低负载条件下(4 w t%),表现出-40.1 d B(2.0 mm)的反射损耗和6.4 GHz(2.4 mm)的有效吸收带宽.该工作提出了一种新型LaOCl/LaFeO_(3)纳米纤维吸波材料,并为阻抗匹配调控和电磁吸波性能优化开辟了新策略.
基金supported by the National Natural Science Foundation of China (Grant No. 10972103)the Ph.D. Programs Foundation of Ministry of Education of China (Grant No. 20093218110004)+1 种基金the Funding of Jiangsu Innovation Program for Graduate Education (Grant No.CXZZ11_0191)Funding for Outstanding Doctoral Dissertation in NUAA (Grant No. BCXJ11-03)
文摘This paper is to study the two-dimensional stress distribution of a finite functionally graded material (FGM) plate with a circular hole under arbitrary constant loads. Using the method of piece-wise homogeneous layers, the stress analysis of the finite FGM plate having radial arbitrary elastic properties is made based on the complex variable method combined with the least square boundary collocation technique. Numerical results of stress distribution around the hole are then presented for different loading conditions, different material properties and different plate sizes, respectively. It is shown that the stress concentration in the finite plate is generally enhanced compared with the case of an infinite plate, but it can be significantly reduced by choosing proper change ways of the radial elastic modulus.
基金the support from National Natural Science Foundation of China(Grant No.11872139)Nian Zhou appreciates the supportfrom Guizhou Provincial Departmentof Education(Grant No.KY[2021]255).
文摘Ductile fracture generally relates to microscopic voiding and to strain localization in metallic materials.When the void size is reduced to the nanoscale,size effects often lead to a different macroscopic plastic behavior from that established for the same material with larger voids.For example,irradiation of metallic materials can generate a large number of voids at the nanoscale,leading to complex deformation behaviors.The present work advances the understanding of strain localization in nanoporous metallic materials,connecting both the microscopic(nano-)and macroscopic scales.To explore the physical mechanisms at the nanoscale,molecular dynamics(MD)simulations were here carried out,capturing multiple nanovoids explicitly.Then,a homogenized continuum theory based in Gurson's constitutive framework is proposed,which enables us to explore how localized behavior at the macroscopic scale evolves.The homogenized model incorporates the surface tension associated with nanosized void.The importance of this surface tension is illustrated by several parametric studies on the conditions of localization,when a specimen is subjected to uniaxial tension.Our parametric studies show that for smaller nanovoid sizes,and for a hardening matrix material,shear localization onset is delayed.Our proposed homogenization model was then used to predict localization behavior captured by our MD simulation.The yield stress and the localization strain predicted by our continuum model are in general agreement with the trends obtained by MD simulation.Moreover,based on our present study,experimental results of shear failure strain vs.dose of irradiation for several metals could be qualitatively explained rather successfully.Our model can therefore help shed light on prolonging the operation limits and the lifetime of irradiated metallic materials under complex loading conditions.
