The crack tip strain gauge method in the compliance technique was used to determine the opening load of notched crack of axle steel,and the nonlinear finite element ADINA program, to which the cyclic stress-strain cur...The crack tip strain gauge method in the compliance technique was used to determine the opening load of notched crack of axle steel,and the nonlinear finite element ADINA program, to which the cyclic stress-strain curve of axle steel was applied,was used to analyze the stress-strain field ahead of the crack tip and the opening load of notched crack.The results of both the compliance technique and the numerical method were in good agreement.In this pa- per,the concept of the sensitive point is proposed and the key to the determination of the crack opening load in the experiment is to place a strain gauge at sensitive point.It is certified by both experimental and numerical methods that the sensitive point has the best linear relation- ship character and the value of strain is much greater.展开更多
The accurate simulation of wave propagation in real media requires properly taking the attenuation into account,which leads to wave dissipation together with its causal companion,wave dispersion.In this study,to obtai...The accurate simulation of wave propagation in real media requires properly taking the attenuation into account,which leads to wave dissipation together with its causal companion,wave dispersion.In this study,to obtain a weak formulation of heterogenous viscoacoustic wave propagation in an infinite domain,the viscoacoustic medium is first characterized by its frequency-dependent complex bulk compliance instead of the classically used complex bulk modulus.Then,a mechanical model using serially connected standard linear solids(SSLS)is built to obtain the rational approximation of the complex bulk compliance whose parameters are calculated via an adapted nonlinear optimization method.Utilizing the obtained bulk compliance-based constitutive relation,a novel second-order viscoacoustic wave equation in the frequency domain is derived,of which the weak formulation can be physically explained as the virtual work equation and can thus be discretized using a continuous spectral element method in space.Additionally,a new method is introduced to address the convolution terms involved in the inverse Fourier transform,whose accurate time integration can then be achieved using an explicit time scheme,which avoids the transient growth that exists in the classical method.The resulting full time-space decoupling scheme can handle wave propagation in arbitrary heterogeneous media.Moreover,to treat the wave propagation in an infinite domain,a perfectly matched layer in weak formulation is derived for the truncation of the infinite domain via complex coordinate stretching of the virtual work equation.With only minor modification,the resulting perfectly matched layer can be implemented using the same time scheme as for the wave equation inside the truncated domain.The accuracy,numerical stability,and versatility of the new proposed scheme are demonstrated with numerical examples.展开更多
Measuring the internal stress of Al alloy forgings accurately is critical for controlling the deformation during the subsequent machine process.In this work,the crack compliance method was used to calculate the intern...Measuring the internal stress of Al alloy forgings accurately is critical for controlling the deformation during the subsequent machine process.In this work,the crack compliance method was used to calculate the internal residual stress of Al-Cu high strength alloys,and the effect of various model parameters of crack compliance method on the calculated precision was studied by combining the numerical simulation and experimental method.The results show that the precision first increased and then decreased with increasing the crack range.The decreased precision when using a high crack range was due to the strain fluctuation during the machining process,and the optimized crack range was 71%of the thickness of forgings.Low orders of Legendre polynomial can result in residual stress curve more smooth,while high orders led to the occurrence of distortion.The Tikhonov regularization method effectively suppressed the distortion of residual stress caused by the fluctuation of strain data,which significantly improved the precision.In addition,The crack compliance method with optimized parameters was used to measure the residual stress of Al-Cu alloy with different quenching methods.The calculated results demonstrated that the distribution of residual stress was obtained accurately.展开更多
Boundary element compliance matrix (BEM) method to deal with 3D elastic frictional contact problem was presented, and its calculation method and convergence criteria were discussed. It has the advantages of both bound...Boundary element compliance matrix (BEM) method to deal with 3D elastic frictional contact problem was presented, and its calculation method and convergence criteria were discussed. It has the advantages of both boundary element method and compliance matrix methods: small number of inputting data, simple and convenient model, precise solution, short calculating time and requirements for a small quantity of computer memory. In comparison to the other BEM with friction problems, we obtain more precise solution and less iteration times. The effect of friction coefficient on contact area. contace state, and relative displacement, normal and tangential stress was analyzed by two examples. And because of the quickness of calculation of program and efficient method, we visualize the result in virtual reality (VR) environment. We grant the real time of VR and provide more immersion to users who ware the VR device.展开更多
During the implementation of CO_(2) fracturing for oil and gas development,the force transfer effect caused by the unsteady flow of high-pressure CO_(2) fluid can lead to forced vibration of the tubing and ensuing str...During the implementation of CO_(2) fracturing for oil and gas development,the force transfer effect caused by the unsteady flow of high-pressure CO_(2) fluid can lead to forced vibration of the tubing and ensuing structural fatigue.In this study,a forced vibration analysis of tubing under CO_(2) fracturing conditions is carried out by taking into account the fluid-structure coupling and related interaction forces by means of the method of characteristics(MOC).The results show that for every 1 m^(3)/min increase in pumping displacement,the fluid flow rate increases up to 3.67 m/s.The flow pressure in the pipe tends to be consistent with the pumping pressure at the initial stage and then decreases with an increase in the pump starting time.When the pumping pressure increases by 10 MPa,the additional stress in the tubing increases by 11.8%,and the peak value of the additional stress at the bottom of the well is the largest.The temperature in the tubing grows with well depth,which causes a phase change in CO_(2) due to heat absorption.At this time the pressure in the tubing decreases,the fluid flow rate increases by about 1.12 m/s,and the additional stress grows by about 1.5 MPa.展开更多
Despite of the limitation in modeling infinite space, the finite element method(FEM) is one of the most used tools to numerically study the geotechnical problems regarding the capacity of simulating different geometri...Despite of the limitation in modeling infinite space, the finite element method(FEM) is one of the most used tools to numerically study the geotechnical problems regarding the capacity of simulating different geometries, conditions and material behaviors. A kind of absorbing layer named perfectly matched layer(PML) has been applied to modeling the radiation damping using FEM, which makes the dynamic analysis of soil-structure interaction more accurate. The PML is capable of absorbing incident waves under any angle and frequency, ensuring them to pass through the model boundaries without reflection.In this context, a new FEM program has been written and the PML formula has been implemented by rewriting the dynamic equation of motion and deriving new properties for the quadrilateral elements.The analysis of soil-foundation interaction by applying the PML is validated by the evaluation of impedance/compliance functions for different ground conditions. The results obtained from the PML model match the extended mesh results, even though the domain is small enough that other types of absorbing boundaries can reflect waves back to the foundation. The mechanism of the wave propagation in the region shows that the forced vibrations can be fully absorbed and damped by the boundaries surrounded by PMLs which is the role of radiation damping in FEM modeling.展开更多
An efficient finite element model of involute helical gear is presented. A program based on compliance matrix method is developed for the calculation of instantaneous meshing stiffness, and the relationship between th...An efficient finite element model of involute helical gear is presented. A program based on compliance matrix method is developed for the calculation of instantaneous meshing stiffness, and the relationship between the rate of meshing stiffness and overlap ratio is given. On the basis of stiffness calculation, an optimization program for the optimal design of profile modification is developed according to the principle of internal point punishment function method.展开更多
The mathematical model of current methods for determining load distribution along contact lines of the instantaneously engaged teeth of gears has a defect that its numerical solution is not unique. In order to overcom...The mathematical model of current methods for determining load distribution along contact lines of the instantaneously engaged teeth of gears has a defect that its numerical solution is not unique. In order to overcome this defect, a new method based on three-dimensional finite element compliance matrix method improved by smoothing method is presented. Calculated examples of helical gears show that the new method can calculate tooth load distribution accurately and agree well with the results of experiments.展开更多
目的分析基于STEAM[S(science),T(technology),E(engineering),A(art),M(mathematics)]理念联合以问题为基础的教学法(problem base learning,PBL)在急诊医学教学中应用效果。方法选择2021年6月—2022年6月滨州医学院急诊科80名本临床...目的分析基于STEAM[S(science),T(technology),E(engineering),A(art),M(mathematics)]理念联合以问题为基础的教学法(problem base learning,PBL)在急诊医学教学中应用效果。方法选择2021年6月—2022年6月滨州医学院急诊科80名本临床医学专业实习生为研究对象,将其随机分为对照组、试验组,各40名。对照组接受传统教学,试验组接受基于STEAM理念联合PBL教学法。对比2组教学前后理论知识及实践操作考试成绩、实习生对教学的满意度、学习依从度及教学前后实习生职业特质评分。结果教学前,2组考核成绩对比,差异无统计学意义(P>0.05);教学3个月后,2组基础理论、实践操作考核成绩均明显提升,但试验组提升幅度更大,差异有统计学意义(P<0.001)。试验组实习生学习依从性(97.50%)高于对照组(85.00%),差异有统计学意义(P<0.001)。试验组教学方法、学术能力、带教态度管理质量评分高于对照组,差异有统计学意义(P<0.001)。教学前,2组实习生职业特质评分对比,差异无统计学意义(P>0.05);教学3个月后,试验组评分高于对照组,差异有统计学意义(P<0.001)。结论在急诊医学教学中,基于STEAM理念联合PBL教学法有利于提升实习生的综合能力,提高理论实践成绩和学习依从性。展开更多
Double-scale model for three-dimension-4 directional（3D-4d） braided C/SiC composites has been proposed to investigate its elastic properties. The double-scale model involves micro-scale that takes fiber/ matrix/poro...Double-scale model for three-dimension-4 directional（3D-4d） braided C/SiC composites has been proposed to investigate its elastic properties. The double-scale model involves micro-scale that takes fiber/ matrix/porosity in fibers tows into consideration with unit cell which considers the 3D-4d braiding structure. Micro-optical photographs of composites have been taken to study the braided structure. Then a parameterized finite element model that reflects the structure of 3D-4d braided composites is proposed. Double-scale elastic modulus prediction model is developed to predict the elastic properties of 3D-4d braided C/SiC composites. Stiffness and eompliance-averaging method and energy method are adopted to predict the elastic properties of composites. Static-tension experiments have been conducted to investigate the elastic modulus of 3D-4d braided C/SiC composites. Finally, the effect of micro-porosity in fibers tows on the elastic modulus of 3D-4d braided C/SiC composites has been studied. According to the conclusion of this thesis, elastic modulus predicted by energy method and stiffness-averaging method both find good agreement with the experimental values, when taking the micro-porosity in fibers tows into consideration. Differences between the theoretical and experimental values become smaller.展开更多
文摘The crack tip strain gauge method in the compliance technique was used to determine the opening load of notched crack of axle steel,and the nonlinear finite element ADINA program, to which the cyclic stress-strain curve of axle steel was applied,was used to analyze the stress-strain field ahead of the crack tip and the opening load of notched crack.The results of both the compliance technique and the numerical method were in good agreement.In this pa- per,the concept of the sensitive point is proposed and the key to the determination of the crack opening load in the experiment is to place a strain gauge at sensitive point.It is certified by both experimental and numerical methods that the sensitive point has the best linear relation- ship character and the value of strain is much greater.
基金National Natural Science Foundation of China under Grant No.U2039209the National Key R&D Program of China under Grant No.2022YFC3004303+1 种基金the Heilongjiang Natural Science Foundation for Distinguished Young Scholars under Grant No.JQ2022E006Heilongjiang Natural Science Foundation Joint Guidance Project under Grant No.LH2021E122。
文摘The accurate simulation of wave propagation in real media requires properly taking the attenuation into account,which leads to wave dissipation together with its causal companion,wave dispersion.In this study,to obtain a weak formulation of heterogenous viscoacoustic wave propagation in an infinite domain,the viscoacoustic medium is first characterized by its frequency-dependent complex bulk compliance instead of the classically used complex bulk modulus.Then,a mechanical model using serially connected standard linear solids(SSLS)is built to obtain the rational approximation of the complex bulk compliance whose parameters are calculated via an adapted nonlinear optimization method.Utilizing the obtained bulk compliance-based constitutive relation,a novel second-order viscoacoustic wave equation in the frequency domain is derived,of which the weak formulation can be physically explained as the virtual work equation and can thus be discretized using a continuous spectral element method in space.Additionally,a new method is introduced to address the convolution terms involved in the inverse Fourier transform,whose accurate time integration can then be achieved using an explicit time scheme,which avoids the transient growth that exists in the classical method.The resulting full time-space decoupling scheme can handle wave propagation in arbitrary heterogeneous media.Moreover,to treat the wave propagation in an infinite domain,a perfectly matched layer in weak formulation is derived for the truncation of the infinite domain via complex coordinate stretching of the virtual work equation.With only minor modification,the resulting perfectly matched layer can be implemented using the same time scheme as for the wave equation inside the truncated domain.The accuracy,numerical stability,and versatility of the new proposed scheme are demonstrated with numerical examples.
基金Project(51875583)supported by the National Natural Science Foundation of ChinaProject(zzyjkt2018-03)supported by the State Key Laboratory of High Performance Complex Manufacturing,China。
文摘Measuring the internal stress of Al alloy forgings accurately is critical for controlling the deformation during the subsequent machine process.In this work,the crack compliance method was used to calculate the internal residual stress of Al-Cu high strength alloys,and the effect of various model parameters of crack compliance method on the calculated precision was studied by combining the numerical simulation and experimental method.The results show that the precision first increased and then decreased with increasing the crack range.The decreased precision when using a high crack range was due to the strain fluctuation during the machining process,and the optimized crack range was 71%of the thickness of forgings.Low orders of Legendre polynomial can result in residual stress curve more smooth,while high orders led to the occurrence of distortion.The Tikhonov regularization method effectively suppressed the distortion of residual stress caused by the fluctuation of strain data,which significantly improved the precision.In addition,The crack compliance method with optimized parameters was used to measure the residual stress of Al-Cu alloy with different quenching methods.The calculated results demonstrated that the distribution of residual stress was obtained accurately.
基金Natural Science Foundation of China(No.5 98895 0 5 )
文摘Boundary element compliance matrix (BEM) method to deal with 3D elastic frictional contact problem was presented, and its calculation method and convergence criteria were discussed. It has the advantages of both boundary element method and compliance matrix methods: small number of inputting data, simple and convenient model, precise solution, short calculating time and requirements for a small quantity of computer memory. In comparison to the other BEM with friction problems, we obtain more precise solution and less iteration times. The effect of friction coefficient on contact area. contace state, and relative displacement, normal and tangential stress was analyzed by two examples. And because of the quickness of calculation of program and efficient method, we visualize the result in virtual reality (VR) environment. We grant the real time of VR and provide more immersion to users who ware the VR device.
基金funded by National Natural Science Foundation of China(Grant No.52105209)funded by the National Engineering Research Centre for Oil and Gas Drilling and Completion Technology(Grant No.F2023199).
文摘During the implementation of CO_(2) fracturing for oil and gas development,the force transfer effect caused by the unsteady flow of high-pressure CO_(2) fluid can lead to forced vibration of the tubing and ensuing structural fatigue.In this study,a forced vibration analysis of tubing under CO_(2) fracturing conditions is carried out by taking into account the fluid-structure coupling and related interaction forces by means of the method of characteristics(MOC).The results show that for every 1 m^(3)/min increase in pumping displacement,the fluid flow rate increases up to 3.67 m/s.The flow pressure in the pipe tends to be consistent with the pumping pressure at the initial stage and then decreases with an increase in the pump starting time.When the pumping pressure increases by 10 MPa,the additional stress in the tubing increases by 11.8%,and the peak value of the additional stress at the bottom of the well is the largest.The temperature in the tubing grows with well depth,which causes a phase change in CO_(2) due to heat absorption.At this time the pressure in the tubing decreases,the fluid flow rate increases by about 1.12 m/s,and the additional stress grows by about 1.5 MPa.
文摘Despite of the limitation in modeling infinite space, the finite element method(FEM) is one of the most used tools to numerically study the geotechnical problems regarding the capacity of simulating different geometries, conditions and material behaviors. A kind of absorbing layer named perfectly matched layer(PML) has been applied to modeling the radiation damping using FEM, which makes the dynamic analysis of soil-structure interaction more accurate. The PML is capable of absorbing incident waves under any angle and frequency, ensuring them to pass through the model boundaries without reflection.In this context, a new FEM program has been written and the PML formula has been implemented by rewriting the dynamic equation of motion and deriving new properties for the quadrilateral elements.The analysis of soil-foundation interaction by applying the PML is validated by the evaluation of impedance/compliance functions for different ground conditions. The results obtained from the PML model match the extended mesh results, even though the domain is small enough that other types of absorbing boundaries can reflect waves back to the foundation. The mechanism of the wave propagation in the region shows that the forced vibrations can be fully absorbed and damped by the boundaries surrounded by PMLs which is the role of radiation damping in FEM modeling.
文摘An efficient finite element model of involute helical gear is presented. A program based on compliance matrix method is developed for the calculation of instantaneous meshing stiffness, and the relationship between the rate of meshing stiffness and overlap ratio is given. On the basis of stiffness calculation, an optimization program for the optimal design of profile modification is developed according to the principle of internal point punishment function method.
文摘The mathematical model of current methods for determining load distribution along contact lines of the instantaneously engaged teeth of gears has a defect that its numerical solution is not unique. In order to overcome this defect, a new method based on three-dimensional finite element compliance matrix method improved by smoothing method is presented. Calculated examples of helical gears show that the new method can calculate tooth load distribution accurately and agree well with the results of experiments.
文摘目的分析基于STEAM[S(science),T(technology),E(engineering),A(art),M(mathematics)]理念联合以问题为基础的教学法(problem base learning,PBL)在急诊医学教学中应用效果。方法选择2021年6月—2022年6月滨州医学院急诊科80名本临床医学专业实习生为研究对象,将其随机分为对照组、试验组,各40名。对照组接受传统教学,试验组接受基于STEAM理念联合PBL教学法。对比2组教学前后理论知识及实践操作考试成绩、实习生对教学的满意度、学习依从度及教学前后实习生职业特质评分。结果教学前,2组考核成绩对比,差异无统计学意义(P>0.05);教学3个月后,2组基础理论、实践操作考核成绩均明显提升,但试验组提升幅度更大,差异有统计学意义(P<0.001)。试验组实习生学习依从性(97.50%)高于对照组(85.00%),差异有统计学意义(P<0.001)。试验组教学方法、学术能力、带教态度管理质量评分高于对照组,差异有统计学意义(P<0.001)。教学前,2组实习生职业特质评分对比,差异无统计学意义(P>0.05);教学3个月后,试验组评分高于对照组,差异有统计学意义(P<0.001)。结论在急诊医学教学中,基于STEAM理念联合PBL教学法有利于提升实习生的综合能力,提高理论实践成绩和学习依从性。
基金Funded by the National Basic Research Program of China,National Natural Science Foundation of China(No.51075204)Funding of Jiangsu Innovation Program for Graduate Education(No.CXLX13_165)+2 种基金the Fundamental Research Funds for the Central Universities,Aeronautical Science Foundation of China(No.2012ZB52026)Research Fund for the Doctoral Program of Higher Education of China(No.20070287039)NUAA Research Funding(No.NZ2012106)
文摘Double-scale model for three-dimension-4 directional（3D-4d） braided C/SiC composites has been proposed to investigate its elastic properties. The double-scale model involves micro-scale that takes fiber/ matrix/porosity in fibers tows into consideration with unit cell which considers the 3D-4d braiding structure. Micro-optical photographs of composites have been taken to study the braided structure. Then a parameterized finite element model that reflects the structure of 3D-4d braided composites is proposed. Double-scale elastic modulus prediction model is developed to predict the elastic properties of 3D-4d braided C/SiC composites. Stiffness and eompliance-averaging method and energy method are adopted to predict the elastic properties of composites. Static-tension experiments have been conducted to investigate the elastic modulus of 3D-4d braided C/SiC composites. Finally, the effect of micro-porosity in fibers tows on the elastic modulus of 3D-4d braided C/SiC composites has been studied. According to the conclusion of this thesis, elastic modulus predicted by energy method and stiffness-averaging method both find good agreement with the experimental values, when taking the micro-porosity in fibers tows into consideration. Differences between the theoretical and experimental values become smaller.
