According to the Mindlin plate theory and the first-order piston theory,this work obtains accurate closed-form eigensolutions for the flutter problem of three-dimensional(3D)rectangular laminated panels.The governing ...According to the Mindlin plate theory and the first-order piston theory,this work obtains accurate closed-form eigensolutions for the flutter problem of three-dimensional(3D)rectangular laminated panels.The governing differential equations are derived by the Hamilton's variational principle,and then solved by the iterative Separation-of-Variable(i SOV)method,which are applicable to arbitrary combinations of homogeneous Boundary Conditions(BCs).However,only the simply-support,clamped and cantilever panels are considered in this work for the sake of clarity.With the closed-form eigensolutions,the flutter frequency,flutter mode and flutter boundary are presented,and the effect of shear deformation and aerodynamic damping on flutter frequencies is investigated.Besides,the relation between panel energy and the work of aerodynamic load is discussed.The numerical comparisons reveal the following.(A)The flutter eigenvalues obtained by the present method are accurate,validated by the Finite Element Method(FEM)and the Galerkin method.(B)When the span-chord ratio is larger than 3,simplifying a 3D panel to 2D(two-dimensional)panel is reasonable and the relative differences of the flutter points predicted by the two models are less than one percent.(C)The reciprocal relationship between the mechanical energy of the panel and the work done by aerodynamic load is verified by using the present flutter eigenvalues and modes,further indicating the high accuracy of the present solutions.(D)The coupling of shear deformation and aerodynamic damping prevents frequency coalescing.展开更多
Considering three longitudinal displacement functions and uniform axial displacement functions for shear lag effect and uniform axial deformation of thin-walled box girder with varying depths,a simple and efficient me...Considering three longitudinal displacement functions and uniform axial displacement functions for shear lag effect and uniform axial deformation of thin-walled box girder with varying depths,a simple and efficient method with high precision to analyze the shear lag effect of thin-walled box girders was proposed.The governing differential equations and boundary conditions of the box girder under lateral loading were derived based on the energy-variational method,and closed-form solutions to stress and deflection corresponding to lateral loading were obtained.Analysis and calculations were carried out with respect to a trapezoidal box girder under concentrated loading or uniform loading and a rectangular box girder under concentrated loading.The analytical results were compared with numerical solutions derived according to the high order finite strip element method and the experimental results.The investigation shows that the closed-form solution is in good agreement with the numerical solutions derived according to the high order finite strip method and the experimental results,and has good stability.Because of the shear lag effect,the stress in cross-section centroid is no longer zero,thus it is not reasonable enough to assume that the strain in cross-section centroid is zero without considering uniform axial deformation.展开更多
Background:The local pivotal method(LPM)utilizing auxiliary data in sample selection has recently been proposed as a sampling method for national forest inventories(NFIs).Its performance compared to simple random samp...Background:The local pivotal method(LPM)utilizing auxiliary data in sample selection has recently been proposed as a sampling method for national forest inventories(NFIs).Its performance compared to simple random sampling(SRS)and LPM with geographical coordinates has produced promising results in simulation studies.In this simulation study we compared all these sampling methods to systematic sampling.The LPM samples were selected solely using the coordinates(LPMxy)or,in addition to that,auxiliary remote sensing-based forest variables(RS variables).We utilized field measurement data(NFI-field)and Multi-Source NFI(MS-NFI)maps as target data,and independent MS-NFI maps as auxiliary data.The designs were compared using relative efficiency(RE);a ratio of mean squared errors of the reference sampling design against the studied design.Applying a method in NFI also requires a proven estimator for the variance.Therefore,three different variance estimators were evaluated against the empirical variance of replications:1)an estimator corresponding to SRS;2)a Grafström-Schelin estimator repurposed for LPM;and 3)a Matérn estimator applied in the Finnish NFI for systematic sampling design.Results:The LPMxy was nearly comparable with the systematic design for the most target variables.The REs of the LPM designs utilizing auxiliary data compared to the systematic design varied between 0.74–1.18,according to the studied target variable.The SRS estimator for variance was expectedly the most biased and conservative estimator.Similarly,the Grafström-Schelin estimator gave overestimates in the case of LPMxy.When the RS variables were utilized as auxiliary data,the Grafström-Schelin estimates tended to underestimate the empirical variance.In systematic sampling the Matérn and Grafström-Schelin estimators performed for practical purposes equally.Conclusions:LPM optimized for a specific variable tended to be more efficient than systematic sampling,but all of the considered LPM designs were less efficient than the systematic sampling design for some target variables.The Grafström-Schelin estimator could be used as such with LPMxy or instead of the Matérn estimator in systematic sampling.Further studies of the variance estimators are needed if other auxiliary variables are to be used in LPM.展开更多
The underhand cut-and-fill mining method is widely employed in underground mines,especially when the quality of surrounding rock mass or ore body is inferior or subjected to high stresses.Such a method typically requi...The underhand cut-and-fill mining method is widely employed in underground mines,especially when the quality of surrounding rock mass or ore body is inferior or subjected to high stresses.Such a method typically requires the construction of sill mats with cemented backfill to provide operators with safe artificial roofs.Accurate estimation of the minimum required strength of the sill mat is crucial to minimize binder consumption and ensure its stability upon base exposure.Over the years,only a few publications were devoted to determining the minimum required cohesion(cmin)of sill mats.None of them considered rock wall closure to be associated with the creep of surrounding rock mass.Moreover,the effect of rock wall closure associated with rock creep on the cminof the sill mat remains unknown.Thus,a series of numerical simulations was performed to fill this gap.The influence of rock creep on the cminof base-exposed sill mat was investigated for the first time.The numerical results indicate that Mitchell’s models could be suitable for sill mats subjected to negligible wall closure.However,this scenario is rare,especially when mine depth is large.In general,the cminof sill mats increases as mine depth increases.Neglecting rock creep would significantly underestimate the cminof sill mats.When mine depth is large and the rock mass exhibits severe creep,cemented backfill with ductile behavior(i.e.,with low stiffness but enough strength)should be considered to reduce binder consumption and prevent crushing failure.In all cases,promptly filling the mined-out stope below the sill mat can improve its stability and reduce its cminvalue.展开更多
感应式磁声成像(Magneto-Acoustic Tomography with Magnetic Induction,MAT-MI)是具备高对比度与高空间分辨率优势的多物理场耦合的新型成像技术,但其逆问题,即重建过程中存在的弧状伪影、噪声敏感干扰限制了成像精度。为此,本文提出...感应式磁声成像(Magneto-Acoustic Tomography with Magnetic Induction,MAT-MI)是具备高对比度与高空间分辨率优势的多物理场耦合的新型成像技术,但其逆问题,即重建过程中存在的弧状伪影、噪声敏感干扰限制了成像精度。为此,本文提出一种时间反演-代数迭代(Algebraic Reconstruction Technique,ART)融合重建算法,通过结合声波传播的物理聚焦机制与正则化数值优化,以声学均匀生物组织模型为研究对象,通过仿真计算得到声压分布,结合时间反演-代数迭代融合重建算法实现声源图像重建。仿真实验表明,本文提出的重建算法能准确有效地重建出声学均匀介质中的声源图像,研究结果对磁声成像实验设计和后续研究提供研究基础。展开更多
In this work,the stress intensity factors(SIFs)for a wide range of semi-elliptical surface cracks with different inclination angles in a cylindrical bar subjected to pure tension were investigated numerically.The main...In this work,the stress intensity factors(SIFs)for a wide range of semi-elliptical surface cracks with different inclination angles in a cylindrical bar subjected to pure tension were investigated numerically.The main parameters considered to evaluate the SIFs were the crack size ratio(a/d),the crack aspect ratio(a/c),and the crack inclination angle(0).The dual-boundary element met hod implemented in software BEASY was used to compute the SIF values for cracks.Furt her more,the general closed-form solutions were proposed to evaluate the corresponding SIFs for Mode I,Mode II and Mode III types of fracture through curve fitting approaches.These solutions can provide accurate and reliable values of stress intensity factors for a crack on a cylindrical bar under pure tension in a rapid way compared to those obtained using computational models.In addition,these results can be used as inputs for failure studies and life evaluations of cracked cylinder under working conditions.展开更多
Based on the complex effective conductivity method, a closed-form expression for the internal impedance of mixed carbon nanotube （CNT） bundles, in which the number of CNTs for a given diameter follows a Gaussian dis...Based on the complex effective conductivity method, a closed-form expression for the internal impedance of mixed carbon nanotube （CNT） bundles, in which the number of CNTs for a given diameter follows a Gaussian distribution, is proposed in this paper. It can appropriately capture the skin effect as well as the temperature effect of mixed CNT bundles. The results of the closed-form expression and the numerical calculation are compared with various mean diameters, standard deviations, and temperatures. It is shown that the proposed model has very high accuracy in the whole frequency range considered, with maximum errors of 1% and 2.3% for the resistance and the internal inductance, respectively. Moreover, by using the proposed model, the high-frequency electrical characteristics of mixed CNT bundles are deeply analyzed to provide helpful design guidelines for their application in future high-performance three-dimensional integrated circuits.展开更多
This treatise analyzes the coupled nonlinear system of the model for the ion sound and Langmuir waves.The modified(G'/G)-expansion procedure is utilized to raise new closed-form wave solutions.Those solutions are ...This treatise analyzes the coupled nonlinear system of the model for the ion sound and Langmuir waves.The modified(G'/G)-expansion procedure is utilized to raise new closed-form wave solutions.Those solutions are investigated through hyperbolic,trigonometric and rational function.The graphical design makes the dynamics of the equations noticeable.It provides the mathematical foundation in diverse sectors of underwater acoustics,electromagnetic wave propagation,design of specific optoelectronic devices and physics quantum mechanics.Herein,we concluded that the studied approach is advanced,meaningful and significant in implementing many solutions of several nonlinear partial differential equations occurring in applied sciences.展开更多
The precipitated silica matting agent was synthesized by chem-deposit method,sodium silicate and sulfurric acid as raw materials,appending dispersant and surfactant.The optimal parameters for the required precipitated...The precipitated silica matting agent was synthesized by chem-deposit method,sodium silicate and sulfurric acid as raw materials,appending dispersant and surfactant.The optimal parameters for the required precipitated silica with excellent properties are temperature 70～85℃,pH value 9,reaction liquid mass concentration 20%,the calcined temperature between 450～480℃.The result shows that the prepared precipitated silica pore volume is 1.0～1.3cm3/g,the partical size is smaller than 10um,D50 approximately 5um.The surface area is 320～430m2/g,the pore size is between 147～388.展开更多
基金support of the National Natural Science Foundation of China(No.12172023)。
文摘According to the Mindlin plate theory and the first-order piston theory,this work obtains accurate closed-form eigensolutions for the flutter problem of three-dimensional(3D)rectangular laminated panels.The governing differential equations are derived by the Hamilton's variational principle,and then solved by the iterative Separation-of-Variable(i SOV)method,which are applicable to arbitrary combinations of homogeneous Boundary Conditions(BCs).However,only the simply-support,clamped and cantilever panels are considered in this work for the sake of clarity.With the closed-form eigensolutions,the flutter frequency,flutter mode and flutter boundary are presented,and the effect of shear deformation and aerodynamic damping on flutter frequencies is investigated.Besides,the relation between panel energy and the work of aerodynamic load is discussed.The numerical comparisons reveal the following.(A)The flutter eigenvalues obtained by the present method are accurate,validated by the Finite Element Method(FEM)and the Galerkin method.(B)When the span-chord ratio is larger than 3,simplifying a 3D panel to 2D(two-dimensional)panel is reasonable and the relative differences of the flutter points predicted by the two models are less than one percent.(C)The reciprocal relationship between the mechanical energy of the panel and the work done by aerodynamic load is verified by using the present flutter eigenvalues and modes,further indicating the high accuracy of the present solutions.(D)The coupling of shear deformation and aerodynamic damping prevents frequency coalescing.
基金Projects(51078355,50938008) supported by the National Natural Science Foundation of ChinaProject(CX2011B093) supported by the Doctoral Candidate Research Innovation Program of Hunan Province, ChinaProject(20117Q008) supported by the Basic Scientific Research Funds for Central Universities of China
文摘Considering three longitudinal displacement functions and uniform axial displacement functions for shear lag effect and uniform axial deformation of thin-walled box girder with varying depths,a simple and efficient method with high precision to analyze the shear lag effect of thin-walled box girders was proposed.The governing differential equations and boundary conditions of the box girder under lateral loading were derived based on the energy-variational method,and closed-form solutions to stress and deflection corresponding to lateral loading were obtained.Analysis and calculations were carried out with respect to a trapezoidal box girder under concentrated loading or uniform loading and a rectangular box girder under concentrated loading.The analytical results were compared with numerical solutions derived according to the high order finite strip element method and the experimental results.The investigation shows that the closed-form solution is in good agreement with the numerical solutions derived according to the high order finite strip method and the experimental results,and has good stability.Because of the shear lag effect,the stress in cross-section centroid is no longer zero,thus it is not reasonable enough to assume that the strain in cross-section centroid is zero without considering uniform axial deformation.
基金the Ministry of Agriculture and Forestry key project“Puuta liikkeelle ja uusia tuotteita metsästä”(“Wood on the move and new products from forest”)Academy of Finland(project numbers 295100 , 306875).
文摘Background:The local pivotal method(LPM)utilizing auxiliary data in sample selection has recently been proposed as a sampling method for national forest inventories(NFIs).Its performance compared to simple random sampling(SRS)and LPM with geographical coordinates has produced promising results in simulation studies.In this simulation study we compared all these sampling methods to systematic sampling.The LPM samples were selected solely using the coordinates(LPMxy)or,in addition to that,auxiliary remote sensing-based forest variables(RS variables).We utilized field measurement data(NFI-field)and Multi-Source NFI(MS-NFI)maps as target data,and independent MS-NFI maps as auxiliary data.The designs were compared using relative efficiency(RE);a ratio of mean squared errors of the reference sampling design against the studied design.Applying a method in NFI also requires a proven estimator for the variance.Therefore,three different variance estimators were evaluated against the empirical variance of replications:1)an estimator corresponding to SRS;2)a Grafström-Schelin estimator repurposed for LPM;and 3)a Matérn estimator applied in the Finnish NFI for systematic sampling design.Results:The LPMxy was nearly comparable with the systematic design for the most target variables.The REs of the LPM designs utilizing auxiliary data compared to the systematic design varied between 0.74–1.18,according to the studied target variable.The SRS estimator for variance was expectedly the most biased and conservative estimator.Similarly,the Grafström-Schelin estimator gave overestimates in the case of LPMxy.When the RS variables were utilized as auxiliary data,the Grafström-Schelin estimates tended to underestimate the empirical variance.In systematic sampling the Matérn and Grafström-Schelin estimators performed for practical purposes equally.Conclusions:LPM optimized for a specific variable tended to be more efficient than systematic sampling,but all of the considered LPM designs were less efficient than the systematic sampling design for some target variables.The Grafström-Schelin estimator could be used as such with LPMxy or instead of the Matérn estimator in systematic sampling.Further studies of the variance estimators are needed if other auxiliary variables are to be used in LPM.
基金financially supported by the Project of National Key Research and Development Program of China(No.2022YFE0129200)the Beijing Nova Program(No.20220484057)+3 种基金the China Scholarship Council(No.202010300001)the National Natural Science Foundation of China(No.52304101)financial support from the Natural Sciences and Engineering Research Council of Canada(No.RGPIN-201806902)industrial partners of the Research Institute on Mines and the Environment(No.RIME UQAT-Polytechnique)。
文摘The underhand cut-and-fill mining method is widely employed in underground mines,especially when the quality of surrounding rock mass or ore body is inferior or subjected to high stresses.Such a method typically requires the construction of sill mats with cemented backfill to provide operators with safe artificial roofs.Accurate estimation of the minimum required strength of the sill mat is crucial to minimize binder consumption and ensure its stability upon base exposure.Over the years,only a few publications were devoted to determining the minimum required cohesion(cmin)of sill mats.None of them considered rock wall closure to be associated with the creep of surrounding rock mass.Moreover,the effect of rock wall closure associated with rock creep on the cminof the sill mat remains unknown.Thus,a series of numerical simulations was performed to fill this gap.The influence of rock creep on the cminof base-exposed sill mat was investigated for the first time.The numerical results indicate that Mitchell’s models could be suitable for sill mats subjected to negligible wall closure.However,this scenario is rare,especially when mine depth is large.In general,the cminof sill mats increases as mine depth increases.Neglecting rock creep would significantly underestimate the cminof sill mats.When mine depth is large and the rock mass exhibits severe creep,cemented backfill with ductile behavior(i.e.,with low stiffness but enough strength)should be considered to reduce binder consumption and prevent crushing failure.In all cases,promptly filling the mined-out stope below the sill mat can improve its stability and reduce its cminvalue.
文摘感应式磁声成像(Magneto-Acoustic Tomography with Magnetic Induction,MAT-MI)是具备高对比度与高空间分辨率优势的多物理场耦合的新型成像技术,但其逆问题,即重建过程中存在的弧状伪影、噪声敏感干扰限制了成像精度。为此,本文提出一种时间反演-代数迭代(Algebraic Reconstruction Technique,ART)融合重建算法,通过结合声波传播的物理聚焦机制与正则化数值优化,以声学均匀生物组织模型为研究对象,通过仿真计算得到声压分布,结合时间反演-代数迭代融合重建算法实现声源图像重建。仿真实验表明,本文提出的重建算法能准确有效地重建出声学均匀介质中的声源图像,研究结果对磁声成像实验设计和后续研究提供研究基础。
文摘In this work,the stress intensity factors(SIFs)for a wide range of semi-elliptical surface cracks with different inclination angles in a cylindrical bar subjected to pure tension were investigated numerically.The main parameters considered to evaluate the SIFs were the crack size ratio(a/d),the crack aspect ratio(a/c),and the crack inclination angle(0).The dual-boundary element met hod implemented in software BEASY was used to compute the SIF values for cracks.Furt her more,the general closed-form solutions were proposed to evaluate the corresponding SIFs for Mode I,Mode II and Mode III types of fracture through curve fitting approaches.These solutions can provide accurate and reliable values of stress intensity factors for a crack on a cylindrical bar under pure tension in a rapid way compared to those obtained using computational models.In addition,these results can be used as inputs for failure studies and life evaluations of cracked cylinder under working conditions.
基金Project supported by the National Science and Technology Major Project of China(Grant No.2015ZX03001004)the National Natural Science Foundation of China(Grant Nos.61604113,61625403,61334003,61376039,61574104,and 61474088)
文摘Based on the complex effective conductivity method, a closed-form expression for the internal impedance of mixed carbon nanotube （CNT） bundles, in which the number of CNTs for a given diameter follows a Gaussian distribution, is proposed in this paper. It can appropriately capture the skin effect as well as the temperature effect of mixed CNT bundles. The results of the closed-form expression and the numerical calculation are compared with various mean diameters, standard deviations, and temperatures. It is shown that the proposed model has very high accuracy in the whole frequency range considered, with maximum errors of 1% and 2.3% for the resistance and the internal inductance, respectively. Moreover, by using the proposed model, the high-frequency electrical characteristics of mixed CNT bundles are deeply analyzed to provide helpful design guidelines for their application in future high-performance three-dimensional integrated circuits.
文摘This treatise analyzes the coupled nonlinear system of the model for the ion sound and Langmuir waves.The modified(G'/G)-expansion procedure is utilized to raise new closed-form wave solutions.Those solutions are investigated through hyperbolic,trigonometric and rational function.The graphical design makes the dynamics of the equations noticeable.It provides the mathematical foundation in diverse sectors of underwater acoustics,electromagnetic wave propagation,design of specific optoelectronic devices and physics quantum mechanics.Herein,we concluded that the studied approach is advanced,meaningful and significant in implementing many solutions of several nonlinear partial differential equations occurring in applied sciences.
文摘The precipitated silica matting agent was synthesized by chem-deposit method,sodium silicate and sulfurric acid as raw materials,appending dispersant and surfactant.The optimal parameters for the required precipitated silica with excellent properties are temperature 70～85℃,pH value 9,reaction liquid mass concentration 20%,the calcined temperature between 450～480℃.The result shows that the prepared precipitated silica pore volume is 1.0～1.3cm3/g,the partical size is smaller than 10um,D50 approximately 5um.The surface area is 320～430m2/g,the pore size is between 147～388.
