Non-acceleration theorem in a primitive equation system is developed to investigate the influences of waves on the mean flow variation against external forcing. Numerical results show that mechanical forcing overwhel... Non-acceleration theorem in a primitive equation system is developed to investigate the influences of waves on the mean flow variation against external forcing. Numerical results show that mechanical forcing overwhelms thermal forcing in maintaining the mean flow in which the internal mechanical forcing associated with horizontal eddy flux of momentum plays the most important roles. Both internal forcing and external forcing are shown to be active and at the first place for the mean flow variations, whereas the forcing-induced mean meridional circulation is passive and secondary. It is also shown that the effects on mean flow of external mechanical forcing are concentrated in the lower troposphere, whereas those due to wave-mean flow interaction are more important in the upper troposphere. These act together and result in the vertically easterly shear in low latitudes and westerly shear in mid-latitudes. This vertical shear of mean flow is to some extent weakened by thermal forcing.展开更多
明显的流动加速效应对超临界二氧化碳强迫对流传热有重要影响。流动加速因子是表征流动加速效应强度的重要无量纲数,在建立流动加速因子过程中需要用到二氧化碳状态方程。理论分析了选取理想气体状态方程和van der Waals方程对建立的流...明显的流动加速效应对超临界二氧化碳强迫对流传热有重要影响。流动加速因子是表征流动加速效应强度的重要无量纲数,在建立流动加速因子过程中需要用到二氧化碳状态方程。理论分析了选取理想气体状态方程和van der Waals方程对建立的流动加速因子合理性的影响,并结合实验数据进行了评估。结果表明,基于vanderWaals方程建立的流动加速因子可以较好地预测流动加速效应引起的传热恶化区域,而基于理想气体状态方程建立的流动加速因子与实验结果存在较大偏差。分析表明体积膨胀系数和体积压缩系数反映了流动加速现象的本质,以体积膨胀系数和体积压缩系数来建立流动加速因子更合理。展开更多
为了有效快速评估高可靠性长寿命产品在正常应力条件下的可靠性,提出了一种双应力恒加试验Weibull分布型产品置信可靠性评估模型。首先,采用加速寿命试验(accelerated life test,ALT)技术,建立广义Eyring-Weibull可靠性模型,假定试验各...为了有效快速评估高可靠性长寿命产品在正常应力条件下的可靠性,提出了一种双应力恒加试验Weibull分布型产品置信可靠性评估模型。首先,采用加速寿命试验(accelerated life test,ALT)技术,建立广义Eyring-Weibull可靠性模型,假定试验各应力水平组合下Weibull分布的形状参数相同,且尺度参数与各应力水平组合间呈对数线性关系。其次,给出了Weibull分布定时截尾双应力恒加试验的极大似然估计(maximum likelihood estimation,MLE)方法、与似然函数相关的Fisher信息矩阵以及模型参数的渐近协方差矩阵,构造了模型参数和一些可靠性指标的渐近置信区间。最后,通过仿真算例证明了所提方法的可行性。展开更多
A computational fluid dynamics(CFD)solver for a GPU/CPU heterogeneous architecture parallel computing platform is developed to simulate incompressible flows on billion-level grid points.To solve the Poisson equation,t...A computational fluid dynamics(CFD)solver for a GPU/CPU heterogeneous architecture parallel computing platform is developed to simulate incompressible flows on billion-level grid points.To solve the Poisson equation,the conjugate gradient method is used as a basic solver,and a Chebyshev method in combination with a Jacobi sub-preconditioner is used as a preconditioner.The developed CFD solver shows good performance on parallel efficiency,which exceeds 90%in the weak-scalability test when the number of grid points allocated to each GPU card is greater than 2083.In the acceleration test,it is found that running a simulation with 10403 grid points on 125 GPU cards accelerates by 203.6x over the same number of CPU cores.The developed solver is then tested in the context of a two-dimensional lid-driven cavity flow and three-dimensional Taylor-Green vortex flow.The results are consistent with previous results in the literature.展开更多
Numerical properties of the time integration method proposed by the first author of this paper in 2007 are the same as those of the constant average acceleration method （AAM） for linear elastic systems, except that ...Numerical properties of the time integration method proposed by the first author of this paper in 2007 are the same as those of the constant average acceleration method （AAM） for linear elastic systems, except that the capability to capture dynamic loading was not explored. It was found that there were different quadrature equations to predict the next step displacement increment. A modified quadrature equation of this method was derived so that the equation to determine the next step displacement was numerically equivalent to the equation used in the constant AAM. It was verified that the original form of this method, in general, had a better capability to capture dynamic loadings than the constant AAM. This excellent property, in addition to computational efficiency, will help to make this method competitive with general secondorder accurate integration methods.展开更多
Traditional gradient domain seamless image cloning is a time consuming task,requiring the solving of Poisson's equations whenever the shape or position of the cloned region changes.Recently,a more efficient altern...Traditional gradient domain seamless image cloning is a time consuming task,requiring the solving of Poisson's equations whenever the shape or position of the cloned region changes.Recently,a more efficient alternative,the mean-value coordinates(MVCs) based approach,was proposed to interpolate interior pixels by a weighted combination of values along the boundary.However,this approach cannot faithfully preserve the gradient in the cloning region.In this paper,we introduce harmonic cloning,which uses harmonic coordinates(HCs) instead of MVCs in image cloning.Benefiting from the non-negativity and interior locality of HCs,our interpolation generates a more accurate harmonic field across the cloned region,to preserve the results with as high a quality as with Poisson cloning.Furthermore,with optimizations and implementation on a graphic processing unit(GPU),we demonstrate that,compared with the method using MVCs,our harmonic cloning gains better quality while retaining real-time performance.展开更多
The solution of minimum-time feedback optimal control problems is generally achieved using the dynamic programming approach,in which the value function must be computed on numerical grids with a very large number of p...The solution of minimum-time feedback optimal control problems is generally achieved using the dynamic programming approach,in which the value function must be computed on numerical grids with a very large number of points.Classical numerical strategies,such as value iteration(VI)or policy iteration(PI)methods,become very inefficient if the number of grid points is large.This is a strong limitation to their use in real-world applications.To address this problem,the authors present a novel multilevel framework,where classical VI and PI are embedded in a full-approximation storage(FAS)scheme.In fact,the authors will show that VI and PI have excellent smoothing properties,a fact that makes them very suitable for use in multilevel frameworks.Moreover,a new smoother is developed by accelerating VI using Anderson’s extrapolation technique.The effectiveness of our new scheme is demonstrated by several numerical experiments.展开更多
In order to account for the observed cosmic acceleration,a modiGcation of the ansatz for the variation of density in Friedman-Robertson-Walker(FRW)FRW models given by Islam is proposed.The modified ansatz leads to an ...In order to account for the observed cosmic acceleration,a modiGcation of the ansatz for the variation of density in Friedman-Robertson-Walker(FRW)FRW models given by Islam is proposed.The modified ansatz leads to an equation of state which corresponds to that of a variable Chaplygin gas,which in the course of evolution reduces to that of a modified generalized Chaplygin gas(MGCG)and a Chaplygin gas(CG),exhibiting late-time acceleration.展开更多
基金Research Project No.[75-09-01] on medium-range numerical weather forecasts.
文摘 Non-acceleration theorem in a primitive equation system is developed to investigate the influences of waves on the mean flow variation against external forcing. Numerical results show that mechanical forcing overwhelms thermal forcing in maintaining the mean flow in which the internal mechanical forcing associated with horizontal eddy flux of momentum plays the most important roles. Both internal forcing and external forcing are shown to be active and at the first place for the mean flow variations, whereas the forcing-induced mean meridional circulation is passive and secondary. It is also shown that the effects on mean flow of external mechanical forcing are concentrated in the lower troposphere, whereas those due to wave-mean flow interaction are more important in the upper troposphere. These act together and result in the vertically easterly shear in low latitudes and westerly shear in mid-latitudes. This vertical shear of mean flow is to some extent weakened by thermal forcing.
文摘明显的流动加速效应对超临界二氧化碳强迫对流传热有重要影响。流动加速因子是表征流动加速效应强度的重要无量纲数,在建立流动加速因子过程中需要用到二氧化碳状态方程。理论分析了选取理想气体状态方程和van der Waals方程对建立的流动加速因子合理性的影响,并结合实验数据进行了评估。结果表明,基于vanderWaals方程建立的流动加速因子可以较好地预测流动加速效应引起的传热恶化区域,而基于理想气体状态方程建立的流动加速因子与实验结果存在较大偏差。分析表明体积膨胀系数和体积压缩系数反映了流动加速现象的本质,以体积膨胀系数和体积压缩系数来建立流动加速因子更合理。
文摘为了有效快速评估高可靠性长寿命产品在正常应力条件下的可靠性,提出了一种双应力恒加试验Weibull分布型产品置信可靠性评估模型。首先,采用加速寿命试验(accelerated life test,ALT)技术,建立广义Eyring-Weibull可靠性模型,假定试验各应力水平组合下Weibull分布的形状参数相同,且尺度参数与各应力水平组合间呈对数线性关系。其次,给出了Weibull分布定时截尾双应力恒加试验的极大似然估计(maximum likelihood estimation,MLE)方法、与似然函数相关的Fisher信息矩阵以及模型参数的渐近协方差矩阵,构造了模型参数和一些可靠性指标的渐近置信区间。最后,通过仿真算例证明了所提方法的可行性。
基金supported by the National Natural Science Foundation of China (NSFC)Basic Science Center Program for Multiscale Problems in Nonlinear Mechanics’(Grant No. 11988102)NSFC project (Grant No. 11972038)
文摘A computational fluid dynamics(CFD)solver for a GPU/CPU heterogeneous architecture parallel computing platform is developed to simulate incompressible flows on billion-level grid points.To solve the Poisson equation,the conjugate gradient method is used as a basic solver,and a Chebyshev method in combination with a Jacobi sub-preconditioner is used as a preconditioner.The developed CFD solver shows good performance on parallel efficiency,which exceeds 90%in the weak-scalability test when the number of grid points allocated to each GPU card is greater than 2083.In the acceleration test,it is found that running a simulation with 10403 grid points on 125 GPU cards accelerates by 203.6x over the same number of CPU cores.The developed solver is then tested in the context of a two-dimensional lid-driven cavity flow and three-dimensional Taylor-Green vortex flow.The results are consistent with previous results in the literature.
基金Science Council (NSC),Chinese Taipei Under Grant No.NSC-96-2221-E-027-030
文摘Numerical properties of the time integration method proposed by the first author of this paper in 2007 are the same as those of the constant average acceleration method （AAM） for linear elastic systems, except that the capability to capture dynamic loading was not explored. It was found that there were different quadrature equations to predict the next step displacement increment. A modified quadrature equation of this method was derived so that the equation to determine the next step displacement was numerically equivalent to the equation used in the constant AAM. It was verified that the original form of this method, in general, had a better capability to capture dynamic loadings than the constant AAM. This excellent property, in addition to computational efficiency, will help to make this method competitive with general secondorder accurate integration methods.
基金supported in part by the National Natural Science Foundation of China (No. 60903037)the National Basic Research Program (973) of China (No. 2009CB320803)
文摘Traditional gradient domain seamless image cloning is a time consuming task,requiring the solving of Poisson's equations whenever the shape or position of the cloned region changes.Recently,a more efficient alternative,the mean-value coordinates(MVCs) based approach,was proposed to interpolate interior pixels by a weighted combination of values along the boundary.However,this approach cannot faithfully preserve the gradient in the cloning region.In this paper,we introduce harmonic cloning,which uses harmonic coordinates(HCs) instead of MVCs in image cloning.Benefiting from the non-negativity and interior locality of HCs,our interpolation generates a more accurate harmonic field across the cloned region,to preserve the results with as high a quality as with Poisson cloning.Furthermore,with optimizations and implementation on a graphic processing unit(GPU),we demonstrate that,compared with the method using MVCs,our harmonic cloning gains better quality while retaining real-time performance.
文摘The solution of minimum-time feedback optimal control problems is generally achieved using the dynamic programming approach,in which the value function must be computed on numerical grids with a very large number of points.Classical numerical strategies,such as value iteration(VI)or policy iteration(PI)methods,become very inefficient if the number of grid points is large.This is a strong limitation to their use in real-world applications.To address this problem,the authors present a novel multilevel framework,where classical VI and PI are embedded in a full-approximation storage(FAS)scheme.In fact,the authors will show that VI and PI have excellent smoothing properties,a fact that makes them very suitable for use in multilevel frameworks.Moreover,a new smoother is developed by accelerating VI using Anderson’s extrapolation technique.The effectiveness of our new scheme is demonstrated by several numerical experiments.
文摘In order to account for the observed cosmic acceleration,a modiGcation of the ansatz for the variation of density in Friedman-Robertson-Walker(FRW)FRW models given by Islam is proposed.The modified ansatz leads to an equation of state which corresponds to that of a variable Chaplygin gas,which in the course of evolution reduces to that of a modified generalized Chaplygin gas(MGCG)and a Chaplygin gas(CG),exhibiting late-time acceleration.
