The structural system failure probability(SFP) is a valuable tool for evaluating the global safety level of concrete gravity dams.Traditional methods for estimating the failure probabilities are based on defined mathe...The structural system failure probability(SFP) is a valuable tool for evaluating the global safety level of concrete gravity dams.Traditional methods for estimating the failure probabilities are based on defined mathematical descriptions,namely,limit state functions of failure modes.Several problems are to be solved in the use of traditional methods for gravity dams.One is how to define the limit state function really reflecting the mechanical mechanism of the failure mode;another is how to understand the relationship among failure modes and enable the probability of the whole structure to be determined.Performing SFP analysis for a gravity dam system is a challenging task.This work proposes a novel nonlinear finite-element-based SFP analysis method for gravity dams.Firstly,reasonable nonlinear constitutive modes for dam concrete,concrete/rock interface and rock foundation are respectively introduced according to corresponding mechanical mechanisms.Meanwhile the response surface(RS) method is used to model limit state functions of main failure modes through the Monte Carlo(MC) simulation results of the dam-interface-foundation interaction finite element(FE) analysis.Secondly,a numerical SFP method is studied to compute the probabilities of several failure modes efficiently by simple matrix integration operations.Then,the nonlinear FE-based SFP analysis methodology for gravity dams considering correlated failure modes with the additional sensitivity analysis is proposed.Finally,a comprehensive computational platform for interfacing the proposed method with the open source FE code Code Aster is developed via a freely available MATLAB software tool(FERUM).This methodology is demonstrated by a case study of an existing gravity dam analysis,in which the dominant failure modes are identified,and the corresponding performance functions are established.Then,the dam failure probability of the structural system is obtained by the proposed method considering the correlation relationship of main failure modes on the basis of the mechanical mechanism analysis with the MC-FE simulations.展开更多
Precisely quantifying the strength of the proximal femur and accurately assessing hip fracture risk would enable those at high risk to be identified so that preventive interventions could be taken.Development of bette...Precisely quantifying the strength of the proximal femur and accurately assessing hip fracture risk would enable those at high risk to be identified so that preventive interventions could be taken.Development of better measures of femoral strength using the clinically展开更多
A finite element model for the supercavitating underwater vehicle was developed by employing 16-node shell elements of relative degrees of freedom.The nonlinear structural dynamic response was performed by introducing...A finite element model for the supercavitating underwater vehicle was developed by employing 16-node shell elements of relative degrees of freedom.The nonlinear structural dynamic response was performed by introducing the updated Lagrangian formulation.The numerical results indicate that there exists a critical thickness for the supercavitating plain shell for the considered velocity of the vehicle.The structure fails more easily because of instability with the thickness less than the critical value,while the structure maintains dynamic stability with the thickness greater than the critical value.As the velocity of the vehicle increases,the critical thickness for the plain shell increases accordingly.For the considered structural configuration,the critical thicknesses of plain shells are 5 and 7 mm for the velocities of 300 and 400 m/s,respectively.The structural stability is enhanced by using the stiffened configuration.With the shell configuration of nine ring stiffeners,the maximal displacement and von Mises stress of the supercavitating structure decrease by 25% and 17% for the velocity of 300 m/s,respectively.Compared with ring stiffeners,longitudinal stiffeners are more significant to improve structural dynamic performance and decrease the critical value of thickness of the shell for the supercavitating vehicle.展开更多
Nonlinear static analysis of piezoelectric plates has been carried out using nonlinear finite element method considering electro-mechanical coupling,The geometrical nonlinearity has been taken into account and electri...Nonlinear static analysis of piezoelectric plates has been carried out using nonlinear finite element method considering electro-mechanical coupling,The geometrical nonlinearity has been taken into account and electric potential is assumed to be quadratic across the plate thickness,The governing equations are obtained using potential energy and Hamilton's principle that includes elastic and piezoelectric effects.The finite element model is derived based on constitutive equation of piezoelectric material accounting for coupling between elasticity and electric effect using higher order plate elements,Results are presented for piezoelectric plate under different mechanical boundary conditions,Numerical results for the plate are given in dimensionless graphical forms.Effects of boundary conditions on linear and nonlinear response of the plate are also studied.The numerical results obtained by the present model are in good agreement with the available solutions reported in the literature.展开更多
传统有限元法对大坝-不规则地基-库水系统进行建模时存在一定的局限性。基于ABAQUS二次开发接口,实现了比例边界有限元方法(scaled boundary finite element method,SBFEM)与八叉树网格的结合,建立了一种考虑真实地形的高拱坝-不规则地...传统有限元法对大坝-不规则地基-库水系统进行建模时存在一定的局限性。基于ABAQUS二次开发接口,实现了比例边界有限元方法(scaled boundary finite element method,SBFEM)与八叉树网格的结合,建立了一种考虑真实地形的高拱坝-不规则地基-库水系统自动建模方法。利用构建的八叉树比例边界有限元法对某重力坝地震响应进行了数值验证。随后对NG5拱坝系统分别基于平整地基和不规则地基进行线弹性和非线性动力响应分析。结果表明:在地震作用下,相较于简化的平整地基拱坝系统,不规则地基拱坝系统坝顶与坝底横河向相对位移以及第一主应力峰值变化较大,分别增加了73.5%和103.6%;考虑拱坝横缝以及材料非线性的情况下,坝顶与坝底横河向相对位移以及顺河向相对位移和相对速度分别增加了43.9%、32.0%和56.6%,同时边缝的法向开度增加尤为显著,增加了388.9%和381.8%,开度峰值增加了105%,在应力和损伤方面,第一主应力峰值增加了81.6%,损伤较大的区域也沿着坝体底部进行了扩展。展开更多
基金Projects(51409167,51139001,51179066)supported by the National Natural Science Foundation of ChinaProjects(201401022,201501036)supported by the Ministry of Water Resources Public Welfare Industry Research Special Fund,ChinaProjects(GG201532,GG201546)supported by the Scientific and Technological Research for Water Conservancy,Henan Province,China
文摘The structural system failure probability(SFP) is a valuable tool for evaluating the global safety level of concrete gravity dams.Traditional methods for estimating the failure probabilities are based on defined mathematical descriptions,namely,limit state functions of failure modes.Several problems are to be solved in the use of traditional methods for gravity dams.One is how to define the limit state function really reflecting the mechanical mechanism of the failure mode;another is how to understand the relationship among failure modes and enable the probability of the whole structure to be determined.Performing SFP analysis for a gravity dam system is a challenging task.This work proposes a novel nonlinear finite-element-based SFP analysis method for gravity dams.Firstly,reasonable nonlinear constitutive modes for dam concrete,concrete/rock interface and rock foundation are respectively introduced according to corresponding mechanical mechanisms.Meanwhile the response surface(RS) method is used to model limit state functions of main failure modes through the Monte Carlo(MC) simulation results of the dam-interface-foundation interaction finite element(FE) analysis.Secondly,a numerical SFP method is studied to compute the probabilities of several failure modes efficiently by simple matrix integration operations.Then,the nonlinear FE-based SFP analysis methodology for gravity dams considering correlated failure modes with the additional sensitivity analysis is proposed.Finally,a comprehensive computational platform for interfacing the proposed method with the open source FE code Code Aster is developed via a freely available MATLAB software tool(FERUM).This methodology is demonstrated by a case study of an existing gravity dam analysis,in which the dominant failure modes are identified,and the corresponding performance functions are established.Then,the dam failure probability of the structural system is obtained by the proposed method considering the correlation relationship of main failure modes on the basis of the mechanical mechanism analysis with the MC-FE simulations.
基金supported by The HongKong Polytechnic University Research Grants(No.1-BB81)grants from National Natural Science Foundation of China,Nos.10872078 and 10832012
文摘Precisely quantifying the strength of the proximal femur and accurately assessing hip fracture risk would enable those at high risk to be identified so that preventive interventions could be taken.Development of better measures of femoral strength using the clinically
文摘A finite element model for the supercavitating underwater vehicle was developed by employing 16-node shell elements of relative degrees of freedom.The nonlinear structural dynamic response was performed by introducing the updated Lagrangian formulation.The numerical results indicate that there exists a critical thickness for the supercavitating plain shell for the considered velocity of the vehicle.The structure fails more easily because of instability with the thickness less than the critical value,while the structure maintains dynamic stability with the thickness greater than the critical value.As the velocity of the vehicle increases,the critical thickness for the plain shell increases accordingly.For the considered structural configuration,the critical thicknesses of plain shells are 5 and 7 mm for the velocities of 300 and 400 m/s,respectively.The structural stability is enhanced by using the stiffened configuration.With the shell configuration of nine ring stiffeners,the maximal displacement and von Mises stress of the supercavitating structure decrease by 25% and 17% for the velocity of 300 m/s,respectively.Compared with ring stiffeners,longitudinal stiffeners are more significant to improve structural dynamic performance and decrease the critical value of thickness of the shell for the supercavitating vehicle.
文摘Nonlinear static analysis of piezoelectric plates has been carried out using nonlinear finite element method considering electro-mechanical coupling,The geometrical nonlinearity has been taken into account and electric potential is assumed to be quadratic across the plate thickness,The governing equations are obtained using potential energy and Hamilton's principle that includes elastic and piezoelectric effects.The finite element model is derived based on constitutive equation of piezoelectric material accounting for coupling between elasticity and electric effect using higher order plate elements,Results are presented for piezoelectric plate under different mechanical boundary conditions,Numerical results for the plate are given in dimensionless graphical forms.Effects of boundary conditions on linear and nonlinear response of the plate are also studied.The numerical results obtained by the present model are in good agreement with the available solutions reported in the literature.
文摘传统有限元法对大坝-不规则地基-库水系统进行建模时存在一定的局限性。基于ABAQUS二次开发接口,实现了比例边界有限元方法(scaled boundary finite element method,SBFEM)与八叉树网格的结合,建立了一种考虑真实地形的高拱坝-不规则地基-库水系统自动建模方法。利用构建的八叉树比例边界有限元法对某重力坝地震响应进行了数值验证。随后对NG5拱坝系统分别基于平整地基和不规则地基进行线弹性和非线性动力响应分析。结果表明:在地震作用下,相较于简化的平整地基拱坝系统,不规则地基拱坝系统坝顶与坝底横河向相对位移以及第一主应力峰值变化较大,分别增加了73.5%和103.6%;考虑拱坝横缝以及材料非线性的情况下,坝顶与坝底横河向相对位移以及顺河向相对位移和相对速度分别增加了43.9%、32.0%和56.6%,同时边缝的法向开度增加尤为显著,增加了388.9%和381.8%,开度峰值增加了105%,在应力和损伤方面,第一主应力峰值增加了81.6%,损伤较大的区域也沿着坝体底部进行了扩展。
